feat(changelog): What's New page with sidebar badge

Adds a hardcoded changelog (internal/changelog) served via
GET /api/changelog and /api/changelog/unseen-count?since=<iso>, a
/changelog page that renders entries newest-first, and a sidebar
"Neuigkeiten" link with a lime badge showing the count of unseen
entries since the caller's last visit (localStorage stamp).

- internal/changelog: Entry struct, 11 pre-populated entries covering
  everything shipped so far (Dashboard, Projects/Deadlines/Appointments,
  CalDAV, Checklists v2, Glossary, Courts, Invitations, Settings,
  Paliad rename, and the changelog itself).
- Handler: public via auth-gated protected mux. Lexicographic string
  compare treats YYYY-MM-DD entries and ISO 8601 cutoffs symmetrically.
- Sidebar: new sidebar-changelog link before the Einladen button; the
  badge is populated by a fetch on every page load, suppressed on
  /changelog itself to avoid flash, and cleared on visit by stamping
  localStorage in changelog.ts's DOMContentLoaded handler.
- i18n: DE + EN keys for nav, page chrome, and tag labels.
- Unit tests for sort order, copy semantics, and same-day cutoff.

Task: t-paliad-027

internal/changelog/changelog.go

@@ -0,0 +1,146 @@
+// Package changelog holds the hardcoded "What's New" feed.
+//
+// Entries are maintained in source — adding a new one is a struct append
+// plus a deploy, no database migration, no admin UI. The list is kept
+// newest-first by convention; ByDateDesc guarantees that ordering at
+// runtime regardless of how authors insert new entries.
+package changelog
+
+import "sort"
+
+// Tag categorises an entry for filtering and UI styling.
+type Tag string
+
+const (
+	TagFeature Tag = "feature"
+	TagContent Tag = "content"
+	TagFix     Tag = "fix"
+)
+
+// Entry is one visible row in the changelog / one badge-worthy event.
+type Entry struct {
+	Date    string `json:"date"` // ISO 8601, YYYY-MM-DD
+	TitleDE string `json:"title_de"`
+	TitleEN string `json:"title_en"`
+	BodyDE  string `json:"body_de"`
+	BodyEN  string `json:"body_en"`
+	Tag     Tag    `json:"tag"`
+}
+
+// Entries lists everything shipped so far, newest first. Append new rows
+// at the top.
+var Entries = []Entry{
+	{
+		Date:    "2026-04-22",
+		Tag:     TagFeature,
+		TitleDE: "Neuigkeiten",
+		TitleEN: "What's New",
+		BodyDE:  "Diese Seite zeigt, was sich in Paliad tut. Der kleine grüne Punkt in der Seitenleiste meldet sich, wenn es etwas Neues gibt — ein Klick hierher lässt ihn wieder verschwinden.",
+		BodyEN:  "This page shows what's new in Paliad. The small green dot in the sidebar appears whenever there's something new — clicking through to this page clears it.",
+	},
+	{
+		Date:    "2026-04-20",
+		Tag:     TagFeature,
+		TitleDE: "Einstellungen mit Benachrichtigungs-Präferenzen",
+		TitleEN: "Settings with notification preferences",
+		BodyDE:  "Unter Einstellungen lassen sich Profil, CalDAV-Zugang und E-Mail-Benachrichtigungen in drei Tabs verwalten. Fristen-Erinnerungen können pro Art (7 Tage / 1 Tag / überfällig) einzeln ein- oder ausgeschaltet werden.",
+		BodyEN:  "Settings now bundles profile, CalDAV and email notifications in three tabs. Deadline reminders can be toggled per type (7 days / 1 day / overdue) independently.",
+	},
+	{
+		Date:    "2026-04-18",
+		Tag:     TagFeature,
+		TitleDE: "Kolleg:innen per E-Mail einladen",
+		TitleEN: "Invite colleagues by email",
+		BodyDE:  "Die Schaltfläche „Kolleg:in einladen\" in der Seitenleiste öffnet ein Modal und verschickt einen Registrierungslink an eine HLC-E-Mail-Adresse. Einladungsstatus und Tageslimit werden direkt angezeigt.",
+		BodyEN:  "The \"Invite colleague\" button in the sidebar opens a modal and sends a registration link to an HLC email address. Invitation status and daily quota are shown inline.",
+	},
+	{
+		Date:    "2026-04-16",
+		Tag:     TagContent,
+		TitleDE: "Paliad — neuer Name, gleicher Lime",
+		TitleEN: "Paliad — new name, same lime",
+		BodyDE:  "Nach dem Zusammenschluss zu HLC wurde patHoLo zu Paliad. Ein firmenunabhängiger Name, damit die Plattform auch künftige Umbenennungen überlebt. Alte Bookmarks auf patholo.de leiten automatisch weiter.",
+		BodyEN:  "Following the HLC merger, patHoLo became Paliad. A firm-agnostic name so the platform outlives future renames. Old patholo.de bookmarks redirect automatically.",
+	},
+	{
+		Date:    "2026-04-15",
+		Tag:     TagFeature,
+		TitleDE: "Dashboard als Startseite",
+		TitleEN: "Dashboard as landing page",
+		BodyDE:  "Nach dem Login landen Sie jetzt auf einem Dashboard mit Fristen-Ampel, nächsten Terminen und letzter Aktivität — alles gefiltert auf Projekte, die Sie sehen dürfen. Server-gerendert, kein Warten auf Daten.",
+		BodyEN:  "After login you now land on a dashboard with deadline traffic lights, upcoming appointments and recent activity — all scoped to projects you can see. Server-rendered, no data waterfall.",
+	},
+	{
+		Date:    "2026-04-12",
+		Tag:     TagFeature,
+		TitleDE: "Termine + CalDAV-Sync",
+		TitleEN: "Appointments + CalDAV sync",
+		BodyDE:  "Termine lassen sich mit Projekten verknüpfen und optional in den persönlichen Kalender synchronisieren (iCloud, Google, eigener CalDAV-Server). Passwörter werden AES-GCM-verschlüsselt gespeichert.",
+		BodyEN:  "Appointments can be linked to projects and optionally synced to your personal calendar (iCloud, Google, self-hosted CalDAV). Passwords are stored AES-GCM encrypted.",
+	},
+	{
+		Date:    "2026-04-08",
+		Tag:     TagFeature,
+		TitleDE: "Fristen-Verwaltung",
+		TitleEN: "Deadline management",
+		BodyDE:  "Persistente Fristen mit Ampel-Karten, Kalenderansicht und E-Mail-Erinnerungen. Verknüpft mit Projekten, teilbar im Team, abhakbar per Klick.",
+		BodyEN:  "Persistent deadlines with traffic-light cards, a calendar view and email reminders. Linked to projects, shared with the team, completable in one click.",
+	},
+	{
+		Date:    "2026-04-04",
+		Tag:     TagFeature,
+		TitleDE: "Projekte mit Hierarchie",
+		TitleEN: "Hierarchical projects",
+		BodyDE:  "Projekte in vier Ebenen: Mandant → Streit → Patent → Akte. Team-Sichtbarkeit vererbt sich entlang des Baums — ein Team am obersten Knoten sieht alle Unterknoten automatisch.",
+		BodyEN:  "Projects in four levels: Client → Litigation → Patent → Matter. Team visibility is inherited down the tree — a team on the top node automatically sees every descendant.",
+	},
+	{
+		Date:    "2026-03-28",
+		Tag:     TagFeature,
+		TitleDE: "Checklisten v2 — interaktiv",
+		TitleEN: "Checklists v2 — interactive",
+		BodyDE:  "Einreichungs-Checklisten lassen sich jetzt als Instanz pro Akte durchklicken, Fortschritt wird gespeichert, Rücksetzen jederzeit möglich.",
+		BodyEN:  "Filing checklists can now be run as per-matter instances, with saved progress and a reset option.",
+	},
+	{
+		Date:    "2026-03-20",
+		Tag:     TagContent,
+		TitleDE: "Gerichtsverzeichnis",
+		TitleEN: "Court directory",
+		BodyDE:  "Kontaktdaten, Einreichungshinweise und Praxistipps zu UPC-Kammern, deutschen Patentgerichten und dem EPA — durchsuchbar und filterbar nach Typ und Land.",
+		BodyEN:  "Contact details, filing notes and practical hints for UPC divisions, German patent courts and the EPO — searchable and filterable by type and country.",
+	},
+	{
+		Date:    "2026-03-10",
+		Tag:     TagContent,
+		TitleDE: "Patentglossar DE/EN",
+		TitleEN: "Patent glossary DE/EN",
+		BodyDE:  "Über 80 Fachbegriffe aus Litigation, Prosecution, UPC, EPA und SEP/FRAND — zweisprachig mit Definitionen. Fehlende Begriffe lassen sich direkt vorschlagen.",
+		BodyEN:  "Over 80 terms from litigation, prosecution, UPC, EPO and SEP/FRAND — bilingual with definitions. Missing terms can be suggested inline.",
+	},
+}
+
+// All returns a copy of the entry list sorted newest-first by Date.
+// Returning a copy keeps the package-level slice immutable for callers
+// that might otherwise sort it in-place.
+func All() []Entry {
+	out := make([]Entry, len(Entries))
+	copy(out, Entries)
+	sort.SliceStable(out, func(i, j int) bool {
+		return out[i].Date > out[j].Date
+	})
+	return out
+}
+
+// UnseenCount returns how many entries have a Date strictly greater than
+// the given cutoff (ISO 8601, YYYY-MM-DD). An empty cutoff is treated as
+// "never seen" — every entry counts.
+func UnseenCount(since string) int {
+	n := 0
+	for _, e := range Entries {
+		if e.Date > since {
+			n++
+		}
+	}
+	return n
+}

internal/changelog/changelog_test.go

@@ -0,0 +1,45 @@
+package changelog
+
+import "testing"
+
+func TestAll_NewestFirst(t *testing.T) {
+	entries := All()
+	if len(entries) == 0 {
+		t.Fatal("expected at least one entry")
+	}
+	for i := 1; i < len(entries); i++ {
+		if entries[i-1].Date < entries[i].Date {
+			t.Fatalf("entries not sorted newest-first at index %d: %q before %q",
+				i, entries[i-1].Date, entries[i].Date)
+		}
+	}
+}
+
+func TestAll_ReturnsCopy(t *testing.T) {
+	a := All()
+	if len(a) == 0 {
+		t.Skip("no entries")
+	}
+	a[0] = Entry{Date: "1970-01-01"}
+	b := All()
+	if b[0].Date == "1970-01-01" {
+		t.Fatal("All() should return an independent copy")
+	}
+}
+
+func TestUnseenCount(t *testing.T) {
+	if got := UnseenCount(""); got != len(Entries) {
+		t.Fatalf("empty cutoff: want %d, got %d", len(Entries), got)
+	}
+	if got := UnseenCount("9999-12-31"); got != 0 {
+		t.Fatalf("far-future cutoff: want 0, got %d", got)
+	}
+	// An ISO timestamp for the same day as an entry is lexicographically
+	// greater than the bare date, so that entry counts as seen.
+	entries := All()
+	newest := entries[0].Date
+	cutoff := newest + "T10:00:00Z"
+	if got := UnseenCount(cutoff); got != 0 {
+		t.Fatalf("same-day ISO timestamp after entry: want 0 unseen, got %d", got)
+	}
+}

internal/handlers/changelog.go

@@ -0,0 +1,31 @@
+package handlers
+
+import (
+	"net/http"
+
+	"mgit.msbls.de/m/patholo/internal/changelog"
+)
+
+// handleChangelogPage serves the static /changelog HTML shell. The entries
+// are fetched client-side via /api/changelog.
+func handleChangelogPage(w http.ResponseWriter, r *http.Request) {
+	http.ServeFile(w, r, "dist/changelog.html")
+}
+
+// handleChangelogAPI returns every entry, newest first.
+func handleChangelogAPI(w http.ResponseWriter, r *http.Request) {
+	writeJSON(w, http.StatusOK, changelog.All())
+}
+
+// handleChangelogUnseenCount returns how many entries are newer than the
+// ?since=<ISO timestamp> query parameter. Missing / empty since is treated
+// as "never seen" so the badge shows on a user's very first session.
+//
+// ISO 8601 timestamps compare correctly as strings against YYYY-MM-DD
+// entry dates (a timestamp for 2026-04-22T10:00:00Z sorts after the date
+// "2026-04-22", which is what we want — same-day entries posted at 00:00
+// are considered seen by mid-day callers).
+func handleChangelogUnseenCount(w http.ResponseWriter, r *http.Request) {
+	since := r.URL.Query().Get("since")
+	writeJSON(w, http.StatusOK, map[string]int{"count": changelog.UnseenCount(since)})
+}

internal/handlers/handlers.go

@@ -110,6 +110,9 @@ func Register(mux *http.ServeMux, client *auth.Client, giteaAPIToken string, svc
 	protected.HandleFunc("GET /courts", handleCourtsPage)
 	protected.HandleFunc("GET /api/courts", handleCourtsAPI)
 	protected.HandleFunc("POST /api/courts/feedback", handleCourtsFeedback)
+	protected.HandleFunc("GET /changelog", handleChangelogPage)
+	protected.HandleFunc("GET /api/changelog", handleChangelogAPI)
+	protected.HandleFunc("GET /api/changelog/unseen-count", handleChangelogUnseenCount)
 
 	// Phase B (DB-backed) — return 503 if DATABASE_URL unset.
 	protected.HandleFunc("GET /api/deadline-rules", handleListDeadlineRules)