M4 Calendar: publish public .ics links, subscriptions, multi-calendar settings

Calendar (builtin plugin):
- Publish read-only public .ics feed per calendar via vault-sealed token
  (full-detail or free/busy-only); unauthenticated GET /public/{token},
  404 on bad/absent token. Migration calendar0004 adds publish_token,
  publish_busy, subscription_url + partial unique index.
- Subscribe to external iCal (.ics) URLs (SSRF-guarded) as read-only
  calendars; CSRF-guarded POST /subscriptions.
- Settings > Calendars: create/edit/delete, publish toggles with live
  shareable link + copy, Add-account stubs (Google/iCloud/CalDAV, deferred),
  Subscriptions section; default calendar + default reminders; auto-detected
  time zone; color-dropdown contrast fix; 3x-larger edit arrow.
- Left panel: shared Mail-parity sidebar template (.wm-side-*), calendar
  search panel, font/spacing tuning, per-section "+" create shortcut.

Frontend: CalendarOut publish fields, api publish/subscribe, settings keys.
Backend: settings default_calendar + reminder lists.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01U72FZiF1W1pb8XxyWBTREA

frontend/src/i18n/en.ts

@@ -13,6 +13,7 @@ export const en = {
   "common.edit": "Edit",
   "common.close": "Close",
   "common.clear": "Clear",
+  "common.copy": "Copy",
   "common.back": "Back",
   "common.next": "Next",
   "common.signOut": "Sign out",
@@ -226,6 +227,33 @@ export const en = {
   "settings.timeFormat": "Time format",
   "settings.timeFormat24": "24-hour (14:30)",
   "settings.timeFormat12": "12-hour (2:30 PM)",
+  "settings.calendars": "Calendars",
+  "settings.myCalendars": "My calendars",
+  "settings.calendarOptions": "Calendar options",
+  "settings.createCalendar": "Create calendar",
+  "settings.editCalendar": "Edit calendar",
+  "settings.export": "Export",
+  "settings.calendarDisplay": "Calendar display",
+  "settings.default": "Default",
+  "settings.defaultCalendar": "Default calendar",
+  "settings.firstCalendar": "First calendar",
+  "settings.defaultRemindersTimed": "Default reminders for timed events",
+  "settings.defaultRemindersAllday": "Default reminders for all-day events",
+  "settings.addReminder": "Add reminder",
+  "settings.name": "Name",
+  "settings.onlyYou": "Only you can see this calendar.",
+  "settings.publish": "Publish",
+  "settings.publishHint": "Share this calendar (read-only) with anyone.",
+  "settings.fullEventDetails": "Full event details",
+  "settings.freeBusy": "Free/busy information",
+  "settings.addAccountHint": "Connect an external calendar account.",
+  "settings.subscriptions": "Subscriptions",
+  "settings.subscriptionsHint": "Add a read-only calendar from an iCal (.ics) URL.",
+  "settings.subscribe": "Subscribe",
+  "settings.subscribeUrl": "iCal (.ics) URL",
+  "settings.subscribed": "Subscribed",
+  "settings.comingSoon": "Coming soon",
+  "settings.subscribeError": "Couldn't subscribe to that URL.",
   "settings.integrations": "Integrations",
   "settings.jitsi": "Jitsi Meet",
   "settings.jitsiHint":