fix: Phase 1 critical+high fixes (17/18 items)

CRITICAL fixes:
- C1: Error swallowing - throw TransportError on network failure in getEmails/searchEmails
- C2: Recurrence expansion ID delimiter changed from ':' to '::occurrence::'
- C3: Cross-account calendar event UID dedup after multi-account aggregation
- C4: Admin session token revocation via JTI blacklist on logout
- C6: FTS5 schema-drop - add warning log for automatic reindex trigger
- C7: Settings lock - gate updateSetting() with isSettingLocked() check
- C8: Offline push pause - add offline event handler that closes push transports

HIGH fixes:
- H1: Push handler - add ContactCard and FileNode branches
- H2: WS fallback - await state snapshot before reconcileAfterWebSocketFallback
- H3: Auth rate limiting - add checkUserAuthRateLimit to session and token routes
- H4: OAuth logs - strip access_token from error log context
- H7: Template XSS - apply DOMPurify to HTML template body on import
- H8: Secure cookie - derive from x-forwarded-proto, not NODE_ENV
- H9: bcrypt fix - remove bcrypt prefixes from isHashed() so scrypt-only
- H13: calendarTasksEnabled - apply admin gate at runtime in calendar page
- H14: Task mutations - add try/catch error handling to update/delete/toggle
- H18: autoSelectReplyIdentity default changed from false to true

Deferred: P1.3 (C5 auth localStorage encryption) - requires custom Zustand persist adapter.

app/(main)/[locale]/calendar/page.tsx

@@ -99,7 +99,9 @@ export default function CalendarPage() {
     refreshAllSubscriptions, icalSubscriptions,
   } = useCalendarStore();
   const calendarEnabled = usePolicyStore((s) => s.isFeatureEnabled('calendarEnabled'));
-  const { firstDayOfWeek, timeFormat, showWeekNumbers, enableCalendarTasks, showTasksOnCalendar, calendarHoverPreview, showBirthdayCalendar, birthdayCalendarColor, updateSetting } = useSettingsStore();
+  const calendarTasksEnabled = usePolicyStore((s) => s.isFeatureEnabled('calendarTasksEnabled'));
+  const { firstDayOfWeek, timeFormat, showWeekNumbers, enableCalendarTasks: userTasksEnabled, showTasksOnCalendar, calendarHoverPreview, showBirthdayCalendar, birthdayCalendarColor, updateSetting } = useSettingsStore();
+  const enableCalendarTasks = userTasksEnabled && calendarTasksEnabled;
   const sharedCalendarColors = useSettingsStore((s) => s.sharedCalendarColors);
   const setSharedCalendarColor = useSettingsStore((s) => s.setSharedCalendarColor);
   const removeSharedCalendarColor = useSettingsStore((s) => s.removeSharedCalendarColor);