iOS: localization fixes, per-calendar reminders, widget polish

C1 — Localization: route the remaining hardcoded German strings through
L10n (LoginView, ServerSetupView, SettingsView email, EventDetailSheet) so
"System Default" + English device language shows fully English text.

C2 — Per-calendar reminders: parse the new reminders_enabled flag on every
calendar type; CalendarStore persists a reminderDisabledKeys set and passes
it to NotificationScheduler, which skips events of muted calendars (default
and per-event reminders). Filter sheet gains a per-calendar reminder toggle
(leading swipe + bell.slash indicator), reconciled from the server and
synced back via PUT.

C3 — Widgets:
- Shared WidgetTime.range helper; Today / Today & Tomorrow / Three Days /
  Up Next now show start–end instead of only the start time.
- This Week: show up to 6 events per day (was 3) to use the height.
- Two Weeks: mini event-title pills instead of bare dots.
- Two Months: weeks expand to fill the column (no more empty lower third).
- Day & Events: smaller header/strip/rows so content stops clipping.
- Next 5 days → Next 7 days (range + labels), higher row cap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CalendarrWidgets/TodayWidgetView.swift

@@ -74,7 +74,7 @@ struct TodayWidgetView: View {
                 Text(ev.title)
                     .font(.caption.weight(.medium))
                     .lineLimit(1)
-                Text(ev.isAllDay ? WidgetL10n.t("widget.allday", lang) : timeFmt.string(from: ev.start))
+                Text(WidgetTime.range(ev, lang: lang))
                     .font(.caption2)
                     .foregroundStyle(.secondary)
             }