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/prisma/migrations/20260904090000_add_calendar_sync/migration.sql

@@ -0,0 +1,42 @@
+-- CreateEnum
+CREATE TYPE "CalendarSyncSourceType" AS ENUM ('TASK', 'INSPECTION', 'TREATMENT', 'FEEDING', 'HARVEST', 'QUEEN_ASSIGNMENT');
+
+-- CreateEnum
+CREATE TYPE "CalendarSyncStatus" AS ENUM ('PENDING', 'SYNCED', 'FAILED', 'SKIPPED');
+
+-- CreateTable
+CREATE TABLE "CalendarSyncSettings" (
+    "id" TEXT NOT NULL DEFAULT 'singleton',
+    "enabled" BOOLEAN NOT NULL DEFAULT false,
+    "groupId" TEXT,
+    "syncTask" BOOLEAN NOT NULL DEFAULT true,
+    "syncInspection" BOOLEAN NOT NULL DEFAULT true,
+    "syncTreatment" BOOLEAN NOT NULL DEFAULT true,
+    "syncFeeding" BOOLEAN NOT NULL DEFAULT true,
+    "syncHarvest" BOOLEAN NOT NULL DEFAULT true,
+    "syncQueenAssignment" BOOLEAN NOT NULL DEFAULT true,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "CalendarSyncSettings_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateTable
+CREATE TABLE "CalendarSyncOutboxEntry" (
+    "id" TEXT NOT NULL,
+    "sourceType" "CalendarSyncSourceType" NOT NULL,
+    "sourceId" TEXT NOT NULL,
+    "status" "CalendarSyncStatus" NOT NULL DEFAULT 'PENDING',
+    "graphEventId" TEXT,
+    "attempts" INTEGER NOT NULL DEFAULT 0,
+    "lastError" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+
+    CONSTRAINT "CalendarSyncOutboxEntry_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "CalendarSyncOutboxEntry_status_idx" ON "CalendarSyncOutboxEntry"("status");
+
+-- CreateIndex
+CREATE UNIQUE INDEX "CalendarSyncOutboxEntry_sourceType_sourceId_key" ON "CalendarSyncOutboxEntry"("sourceType", "sourceId");