refactor(calendar): t-paliad-224 — retire standalone calendar pages + prune dead code

Delete the four orphan files behind /deadlines/calendar +
/appointments/calendar:
- frontend/src/{deadlines,appointments}-calendar.tsx
- frontend/src/client/{deadlines,appointments}-calendar.ts
The standalone pages were unreachable from the UI since t-paliad-110
(Sidebar/BottomNav point at /events?type=…); their only role was as
bookmark targets.

Handlers in internal/handlers/{deadlines,appointments}_pages.go now
301-redirect to /events?type=…&view=calendar so bookmarks still
work. Route registrations in handlers.go remain unchanged — the
gate + redirect pair gives us the same URL surface with one canonical
renderer.

build.ts: drop the renderDeadlinesCalendar / renderAppointmentsCalendar
imports + entry-point bundle paths + dist HTML writes.

frontend/src/client/paliadin-context.ts: drop the two route-key
matches for the standalone URLs (the client never sees those
pathnames any more — 301 fires server-side).

Dead CSS pruned in frontend/src/styles/global.css (~180 lines):
- .frist-calendar, .frist-cal-{controls,month-label,grid,cell,…}
  block (lines 7464-7613 pre-refactor)
- @media (max-width: 700px) { .frist-cal-cell { min-height: 64px; } }
- .termin-cal-legend{,-item}
- .frist-cal-popup-time
- .frist-cal-dot.events-cal-dot-appointment

All verified by grep across frontend/ + internal/ to have no
non-calendar consumers before deletion.

Dead i18n keys removed (DE + EN + i18n-keys.ts union type):
- deadlines.kalender.{title,heading,subtitle,list,today,empty}
- appointments.kalender.{title,heading,subtitle,list,empty}
- deadlines.list.calendar, appointments.list.calendar (button labels
  on the deleted standalone routes)
- events.calendar.empty (replaced by cal.day.no_entries inside
  mountCalendar's day view)

Per head decisions §11 Q1 + Q8 (drop standalone pages as 301s; drop
dead i18n now).

Tests: go build ./... clean; go test ./internal/... 9 packages pass;
cd frontend && bun run build clean (2535 i18n keys); bun test
frontend/src/client/{calendar,views}/ all 73/73 pass.

internal/handlers/appointments_pages.go

@@ -24,8 +24,13 @@ func handleAppointmentsDetailPage(w http.ResponseWriter, r *http.Request) {
 	http.ServeFile(w, r, "dist/appointments-detail.html")
 }
 
+// handleAppointmentsCalendarPage 301-redirects the legacy standalone
+// calendar route to the canonical /events Kalender tab (t-paliad-224 /
+// m/paliad#55). Counterpart of handleDeadlinesCalendarPage — same
+// reasoning: the standalone page was orphaned in navigation since
+// t-paliad-110, the canonical calendar lives inside /events.
 func handleAppointmentsCalendarPage(w http.ResponseWriter, r *http.Request) {
-	http.ServeFile(w, r, "dist/appointments-calendar.html")
+	http.Redirect(w, r, "/events?type=appointment&view=calendar", http.StatusMovedPermanently)
 }
 
 // handleSettingsPage serves the unified settings page with tabs for

internal/handlers/deadlines_pages.go

@@ -23,6 +23,13 @@ func handleDeadlinesDetailPage(w http.ResponseWriter, r *http.Request) {
 	http.ServeFile(w, r, "dist/deadlines-detail.html")
 }
 
+// handleDeadlinesCalendarPage 301-redirects the legacy standalone
+// calendar route to the canonical /events Kalender tab (t-paliad-224 /
+// m/paliad#55). The standalone page was orphaned in navigation since
+// t-paliad-110 — Sidebar/BottomNav already point at /events?type=…, and
+// the canonical calendar lives inside that page's view chip. The
+// redirect preserves bookmarks and external links without a duplicate
+// rendering pipeline.
 func handleDeadlinesCalendarPage(w http.ResponseWriter, r *http.Request) {
-	http.ServeFile(w, r, "dist/deadlines-calendar.html")
+	http.Redirect(w, r, "/events?type=deadline&view=calendar", http.StatusMovedPermanently)
 }