Add OpenAPI docs, frontend, migrations, and API updates

- OpenAPI: add missing endpoints (add-from-url, subscriptions, public availability)
- OpenAPI: CalendarSubscription schema, Subscriptions tag
- Frontend app
- Migrations: count_for_availability, subscriptions_sync, user_preferences, calendar_settings
- Config, rate limit, auth, calendar, booking, ICS, availability, user service updates

Made-with: Cursor

internal/service/event.go

@@ -414,8 +414,8 @@ func (s *EventService) expandRecurrence(ev repository.Event, rangeStart, rangeEn
 			Title:               ev.Title,
 			Description:         utils.FromPgText(ev.Description),
 			Location:            utils.FromPgText(ev.Location),
-			StartTime:           dtStart,
-			EndTime:             dtStart.Add(duration),
+			StartTime:           occStart,
+			EndTime:             occEnd,
 			Timezone:            ev.Timezone,
 			AllDay:              ev.AllDay,
 			RecurrenceRule:      utils.FromPgText(ev.RecurrenceRule),