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/calendar-sync/calendar-sync.module.ts

@@ -0,0 +1,21 @@
+import { Global, Module } from '@nestjs/common';
+import { CalendarSyncController } from './calendar-sync.controller';
+import { CalendarSyncService } from './calendar-sync.service';
+import { CalendarSyncSettingsService } from './calendar-sync-settings.service';
+import { GraphClientService } from './graph-client.service';
+
+// @Global(): CalendarSyncService.enqueue()/cancel() are called from ~6
+// otherwise-unrelated domain modules (Tasks, Inspections, Treatments,
+// Feedings, Harvests, Queens) - matches WebhooksModule's own @Global()
+// rationale rather than having each of those six modules import this one.
+@Global()
+@Module({
+  controllers: [CalendarSyncController],
+  providers: [
+    CalendarSyncService,
+    CalendarSyncSettingsService,
+    GraphClientService,
+  ],
+  exports: [CalendarSyncService],
+})
+export class CalendarSyncModule {}