refactor(events): t-paliad-224 — fold Kalender tab into mountCalendar()

The /events Kalender view now mounts the canonical mountCalendar()
module from frontend/src/client/calendar/ — same renderer Custom
Views uses for shape=calendar. Drops the events-page-specific
month-grid + popup code path entirely.

What replaces what
- renderCalendar() / openCalPopup() / calDotClass / fmtMonthYear /
  isoDate / itemDateISO and the calYear/calMonth module state →
  one mountCalendar() handle (lazy, urlState=true).
- events-cal-prev / events-cal-next / events-cal-today buttons →
  toolbar in mountCalendar (includes its own 'Heute' button).
- modal popup on cell click → drill-down to day view (matches
  /views; head decision §11 Q2).
- @media min-height shrink on .frist-cal-cell → views-calendar-*
  responsive surface (CSS unchanged from /views).

Behavioural deltas vs pre-refactor
- /events Kalender now persists view+anchor in ?cal_view + ?cal_date
  (head decision §11 Q3) — refresh / share-link safe.
- Pills are kind-coded (deadline / appointment) rather than urgency-
  coded; matches /views (head decision §11 Q4 — drop subtype dot
  colouring, file as follow-up).
- Empty-month message gone; the per-day no-entries state from the
  day-view replaces it (head decision §11 Q8 — drop dead i18n).

Adapter: toCalendarItem() preserves the pre-refactor bucketing rule
— deadlines bucket on due_date, appointments on start_at, both fall
back to event_date.

events.tsx: 31-line calendar subtree (toolbar + grid + modal +
empty hint) reduces to a single host div. mountCalendar fills it
when the user picks Kalender.

frontend/src/client/events.ts

@@ -8,6 +8,7 @@ import {
   type FilterHandle,
 } from "./event-types";
 import { projectIndent } from "./project-indent";
+import { mountCalendar, type CalendarHandle, type CalendarItem } from "./calendar/mount-calendar";
 
 // Two-eyes glyph 👀 inside .approval-pill--icon. m's 2026-05-08 follow-
 // up: "two eyes instead of the one." Emoji rather than SVG keeps the
@@ -157,8 +158,10 @@ let me: Me | null = null;
 let eventTypeFilter: FilterHandle | null = null;
 let eventTypeByID: Map<string, EventType> = new Map();
 let loadedOK = false;
-let calYear = 0;
-let calMonth = 0;
+// Calendar handle is created lazily when /events first switches into the
+// Kalender view (t-paliad-224). The handle owns its own month/week/day
+// state + ?cal_view / ?cal_date URL contract via mountCalendar.
+let calendar: CalendarHandle | null = null;
 
 function urlParams(): URLSearchParams {
   return new URLSearchParams(window.location.search);
@@ -429,12 +432,13 @@ function hideTableAndCalendar() {
   const calWrap = document.getElementById("events-calendar-wrap");
   if (tableWrap) tableWrap.style.display = "none";
   if (calWrap) calWrap.hidden = true;
+  teardownCalendar();
 }
 
 function render() {
   if (!loadedOK) return;
   if (currentView === "calendar") {
-    renderCalendar();
+    renderCalendarView();
   } else {
     renderTable();
   }
@@ -557,135 +561,57 @@ function renderRow(item: EventListItem, showReopen: boolean): string {
   </tr>`;
 }
 
-// itemDateISO returns the per-item bucketing date (YYYY-MM-DD) used when
-// plotting an event onto the calendar. Deadlines bucket on due_date;
-// appointments on start_at's local-date component.
-function itemDateISO(item: EventListItem): string {
+// toCalendarItem adapts an EventListItem to the canonical CalendarItem
+// shape consumed by mountCalendar (t-paliad-224). Bucketing date matches
+// the pre-refactor behaviour: deadlines bucket on due_date (fallback to
+// event_date); appointments bucket on start_at (fallback to event_date).
+function toCalendarItem(item: EventListItem): CalendarItem {
+  let bucketDate: string;
   if (item.type === "deadline") {
-    const src = item.due_date ?? item.event_date;
-    return src.slice(0, 10);
+    bucketDate = item.due_date ?? item.event_date;
+  } else if (item.start_at) {
+    bucketDate = item.start_at;
+  } else {
+    bucketDate = item.event_date;
   }
-  if (!item.start_at) return item.event_date.slice(0, 10);
-  const d = new Date(item.start_at);
-  return `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, "0")}-${String(d.getDate()).padStart(2, "0")}`;
+  return {
+    kind: item.type,
+    id: item.id,
+    title: item.title,
+    event_date: bucketDate,
+    project_id: item.project_id,
+    project_title: item.project_title,
+    project_reference: item.project_reference,
+  };
 }
 
-function isoDate(year: number, month: number, day: number): string {
-  return `${year}-${String(month + 1).padStart(2, "0")}-${String(day).padStart(2, "0")}`;
-}
-
-function fmtMonthYear(year: number, month: number): string {
-  return `${tDyn(`cal.month.${month}`)} ${year}`;
-}
-
-function calDotClass(item: EventListItem): string {
-  // Per-item dot colour. Deadlines reuse the existing urgency palette;
-  // appointments get their own colour so they're visually distinct from
-  // deadlines on a mixed (Beides) calendar.
-  if (item.type === "appointment") return "events-cal-dot-appointment";
-  return urgencyClass(item).replace("frist-urgency-", "frist-urgency-");
-}
-
-function renderCalendar() {
-  const wrap = document.getElementById("events-calendar-wrap")!;
-  const grid = document.getElementById("events-cal-grid")!;
-  const empty = document.getElementById("events-cal-empty") as HTMLElement;
-  const monthLabel = document.getElementById("events-cal-month-label")!;
+function renderCalendarView() {
+  const host = document.getElementById("events-calendar-wrap");
+  if (!host) return;
   const tableEmpty = document.getElementById("events-empty")!;
   const tableEmptyFiltered = document.getElementById("events-empty-filtered")!;
-
-  // Calendar always renders the visible month from allItems, regardless of
-  // pristine vs filtered state — empty calendar is allowed (the per-month
-  // empty hint communicates "no items in this month" without confusing it
-  // with the table-mode "no items at all" empty state).
   tableEmpty.style.display = "none";
   tableEmptyFiltered.style.display = "none";
-  wrap.hidden = false;
+  (host as HTMLElement).hidden = false;
 
-  monthLabel.textContent = fmtMonthYear(calYear, calMonth);
-
-  const firstDay = new Date(calYear, calMonth, 1);
-  const jsWeekday = firstDay.getDay();
-  const offset = (jsWeekday + 6) % 7;
-  const daysInMonth = new Date(calYear, calMonth + 1, 0).getDate();
-  const today = new Date();
-  const todayISO = isoDate(today.getFullYear(), today.getMonth(), today.getDate());
-
-  // Bucket items by ISO date once, so day-cell rendering is O(d) not O(d*n).
-  const byDate = new Map<string, EventListItem[]>();
-  for (const item of allItems) {
-    const iso = itemDateISO(item);
-    const list = byDate.get(iso);
-    if (list) list.push(item);
-    else byDate.set(iso, [item]);
+  const items = allItems.map(toCalendarItem);
+  if (calendar) {
+    calendar.update(items);
+    return;
   }
-
-  const cells: string[] = [];
-  for (let i = 0; i < offset; i++) {
-    cells.push(`<div class="frist-cal-cell frist-cal-cell-empty"></div>`);
-  }
-  for (let day = 1; day <= daysInMonth; day++) {
-    const iso = isoDate(calYear, calMonth, day);
-    const items = byDate.get(iso) ?? [];
-    const isToday = iso === todayISO;
-    const dots = items
-      .slice(0, 4)
-      .map((it) => `<span class="frist-cal-dot ${calDotClass(it)}"></span>`)
-      .join("");
-    const more = items.length > 4 ? `<span class="frist-cal-more">+${items.length - 4}</span>` : "";
-    cells.push(
-      `<div class="frist-cal-cell${isToday ? " frist-cal-today" : ""}${items.length > 0 ? " frist-cal-cell-has" : ""}" data-iso="${iso}">
-        <span class="frist-cal-day">${day}</span>
-        <div class="frist-cal-dots">${dots}${more}</div>
-      </div>`,
-    );
-  }
-  grid.innerHTML = cells.join("");
-
-  grid.querySelectorAll<HTMLElement>(".frist-cal-cell-has").forEach((cell) => {
-    cell.addEventListener("click", () => openCalPopup(cell.dataset.iso!, byDate.get(cell.dataset.iso!) ?? []));
+  // urlState=true: the Kalender tab persists its month/week/day + anchor
+  // in ?cal_view + ?cal_date so a refresh / shared link lands on the same
+  // calendar state (per t-paliad-224 §11 Q3 head decision).
+  calendar = mountCalendar(host as HTMLElement, items, {
+    urlState: true,
+    defaultView: "month",
   });
-
-  const monthStart = isoDate(calYear, calMonth, 1);
-  const monthEnd = isoDate(calYear, calMonth, daysInMonth);
-  const hasInMonth = allItems.some((it) => {
-    const iso = itemDateISO(it);
-    return iso >= monthStart && iso <= monthEnd;
-  });
-  empty.hidden = hasInMonth;
 }
 
-function openCalPopup(iso: string, items: EventListItem[]) {
-  if (items.length === 0) return;
-  const popup = document.getElementById("events-cal-popup") as HTMLElement;
-  const dateEl = document.getElementById("events-cal-popup-date")!;
-  const list = document.getElementById("events-cal-popup-list")!;
-
-  const d = new Date(iso + "T00:00:00");
-  dateEl.textContent = d.toLocaleDateString(getLang() === "de" ? "de-DE" : "en-GB", {
-    weekday: "long",
-    year: "numeric",
-    month: "long",
-    day: "numeric",
-  });
-
-  list.innerHTML = items
-    .map((it) => {
-      const cls = calDotClass(it);
-      const href = it.type === "deadline" ? `/deadlines/${esc(it.id)}` : `/appointments/${esc(it.id)}`;
-      const projectHref = it.project_id ? `/projects/${esc(it.project_id)}` : "";
-      const projectLabel = it.project_reference ?? "";
-      const projectCell = projectHref
-        ? `<a href="${projectHref}" class="frist-cal-popup-akte">${esc(projectLabel)}</a>`
-        : "";
-      return `<li class="frist-cal-popup-item">
-        <span class="frist-cal-dot ${cls}"></span>
-        <a href="${href}" class="frist-cal-popup-title">${rowTypeChip(it)} ${esc(it.title)}</a>
-        ${projectCell}
-      </li>`;
-    })
-    .join("");
-  popup.style.display = "flex";
+function teardownCalendar() {
+  if (!calendar) return;
+  calendar.destroy();
+  calendar = null;
 }
 
 function applyView() {
@@ -706,12 +632,18 @@ function applyView() {
   // Cards view = the original layout (5-card summary + table).
   // List view = no summary cards, table only — gives more vertical space
   //   and matches users' mental model of a flat list.
-  // Calendar view = month grid; cards + table both hidden.
+  // Calendar view = mountCalendar() canon (month/week/day); cards + table
+  //   both hidden. The handle is torn down when the user leaves Kalender
+  //   so its URL state isn't reapplied to other shapes.
   summary.style.display = currentView === "cards" ? "" : "none";
   tableWrap.style.display = currentView === "calendar" ? "none" : "";
   calWrap.hidden = currentView !== "calendar";
 
-  if (currentView === "calendar" && loadedOK) renderCalendar();
+  if (currentView === "calendar") {
+    if (loadedOK) renderCalendarView();
+  } else {
+    teardownCalendar();
+  }
 }
 
 function wireRowHandlers(tbody: HTMLElement) {
@@ -1013,12 +945,10 @@ function initFilters() {
 }
 
 function initView() {
-  // Calendar always opens on the current month — month navigation is
-  // local to the view (cheap pagination, doesn't refetch).
-  const now = new Date();
-  calYear = now.getFullYear();
-  calMonth = now.getMonth();
-
+  // Kalender state (view + anchor) lives inside mountCalendar; no
+  // events-page-level wiring needed. The view chips below switch
+  // between Karten / Liste / Kalender; applyView() handles the
+  // mount + teardown.
   document.querySelectorAll<HTMLButtonElement>("[data-event-view]").forEach((btn) => {
     btn.addEventListener("click", () => {
       const next = btn.dataset.eventView as EventView;
@@ -1028,31 +958,6 @@ function initView() {
       syncURLParams();
     });
   });
-
-  document.getElementById("events-cal-prev")?.addEventListener("click", () => {
-    calMonth -= 1;
-    if (calMonth < 0) { calMonth = 11; calYear -= 1; }
-    renderCalendar();
-  });
-  document.getElementById("events-cal-next")?.addEventListener("click", () => {
-    calMonth += 1;
-    if (calMonth > 11) { calMonth = 0; calYear += 1; }
-    renderCalendar();
-  });
-  document.getElementById("events-cal-today")?.addEventListener("click", () => {
-    const t = new Date();
-    calYear = t.getFullYear();
-    calMonth = t.getMonth();
-    renderCalendar();
-  });
-
-  const popup = document.getElementById("events-cal-popup") as HTMLElement;
-  document.getElementById("events-cal-popup-close")?.addEventListener("click", () => {
-    popup.style.display = "none";
-  });
-  popup?.addEventListener("click", (e) => {
-    if (e.target === popup) popup.style.display = "none";
-  });
 }
 
 function initSummaryCards() {

frontend/src/events.tsx

@@ -236,37 +236,10 @@ export function renderEvents(): string {
                 </table>
               </div>
 
-              <div id="events-calendar-wrap" className="events-calendar-wrap" hidden>
-                <div className="frist-calendar-controls">
-                  <button type="button" id="events-cal-prev" className="btn-secondary btn-small" aria-label="Vorheriger Monat">&larr;</button>
-                  <h2 id="events-cal-month-label" className="frist-cal-month-label" />
-                  <button type="button" id="events-cal-next" className="btn-secondary btn-small" aria-label="N&auml;chster Monat">&rarr;</button>
-                  <button type="button" id="events-cal-today" className="btn-secondary btn-small" data-i18n="deadlines.kalender.today">Heute</button>
-                </div>
-                <div className="frist-calendar">
-                  <div className="frist-cal-weekday" data-i18n="cal.day.mon">Mo</div>
-                  <div className="frist-cal-weekday" data-i18n="cal.day.tue">Di</div>
-                  <div className="frist-cal-weekday" data-i18n="cal.day.wed">Mi</div>
-                  <div className="frist-cal-weekday" data-i18n="cal.day.thu">Do</div>
-                  <div className="frist-cal-weekday" data-i18n="cal.day.fri">Fr</div>
-                  <div className="frist-cal-weekday" data-i18n="cal.day.sat">Sa</div>
-                  <div className="frist-cal-weekday" data-i18n="cal.day.sun">So</div>
-                  <div id="events-cal-grid" className="frist-cal-grid" />
-                </div>
-                <p className="entity-events-empty" id="events-cal-empty" hidden data-i18n="events.calendar.empty">
-                  Keine Eintr&auml;ge im ausgew&auml;hlten Zeitraum.
-                </p>
-              </div>
-
-              <div className="modal-overlay" id="events-cal-popup" style="display:none">
-                <div className="modal-card">
-                  <div className="modal-header">
-                    <h2 id="events-cal-popup-date" />
-                    <button className="modal-close" id="events-cal-popup-close" type="button" aria-label="Close">&times;</button>
-                  </div>
-                  <ul className="frist-cal-popup-list" id="events-cal-popup-list" />
-                </div>
-              </div>
+              {/* Calendar host — mountCalendar() (t-paliad-224) builds the
+                  month/week/day grid + toolbar into this container when
+                  the Kalender view chip is active. Empty until then. */}
+              <div id="events-calendar-wrap" className="events-calendar-wrap" hidden />
 
               <div className="entity-empty" id="events-empty" style="display:none">
                 <h2 data-i18n="events.empty.title">Keine Eintr&auml;ge vorhanden</h2>