feat: sync calendar entries to a Microsoft 365 group calendar

Adds a one-way push (ApiCore -> M365) of Aufgaben/Durchsichten/
Behandlungen/Fütterungen/Ernten/Königinnen-Zuordnungen into the calendar
of a Microsoft 365 group, via the Graph API.

- CalendarSyncModule (app-only client-credentials Graph auth, separate
  from the interactive SSO app registration; new env vars
  M365_CALENDAR_TENANT_ID/_CLIENT_ID/_CLIENT_SECRET).
- Outbox + minute-interval cron worker (CalendarSyncOutboxEntry) instead
  of a synchronous push, since Graph calls are too slow/flaky to block a
  domain create request on; failed syncs retry up to 5 times.
- Per-source-type toggle plus a group-ID field, configurable in
  Verwaltung > Automatisierung > Kalender-Sync (Verwaltung > Backup, an
  env var still wins on those fields where one applies to related config).
- Hooked into Tasks/Inspections/Treatments/Feedings/Harvests/Queens at
  their existing create (and Task update/complete) points; entries render
  as all-day Graph events to avoid timezone ambiguity.
- Documents the design decision in ARCHITECTURE.md (Annahme 9), since
  this is a net-new capability the lastenheft doesn't scope.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

ApiCore-Backend/src/app.module.ts

@@ -29,6 +29,7 @@ import { ProductsModule } from './products/products.module';
 import { BottlingModule } from './bottling/bottling.module';
 import { EquipmentModule } from './equipment/equipment.module';
 import { CalendarModule } from './calendar/calendar.module';
+import { CalendarSyncModule } from './calendar-sync/calendar-sync.module';
 import { NotificationsModule } from './notifications/notifications.module';
 import { StatisticsModule } from './statistics/statistics.module';
 import { WebhooksModule } from './webhooks/webhooks.module';
@@ -79,6 +80,7 @@ import { PermissionsModule } from './auth/permissions/permissions.module';
     BottlingModule,
     EquipmentModule,
     CalendarModule,
+    CalendarSyncModule,
     NotificationsModule,
     StatisticsModule,
     WebhooksModule,