feat: P2-15 cron-based DingTalk/WeCom sync with logging and incremental sync

- Add @nestjs/schedule dependency
- Create SyncLog entity (platform, syncType, status, recordsCount, errorMessage, timestamps)
- Create SyncState entity for tracking lastSyncAt per platform
- SyncService with @Cron('0 2 * * *') daily scheduled sync
- Incremental sync: tracks last_sync_at per platform, passes to integration APIs
- Full/incremental mode determined by existence of prior sync
- SyncController: POST /sync/trigger (manual), GET /sync/logs (history)
- Register SyncModule in AppModule with ScheduleModule

apps/server/package.json

@@ -28,6 +28,7 @@
     "@nestjs/jwt": "^11.0.2",
     "@nestjs/passport": "^11.0.5",
     "@nestjs/platform-express": "^11.1.19",
+    "@nestjs/schedule": "^6.1.3",
     "@nestjs/throttler": "^6.5.0",
     "@nestjs/typeorm": "^11.0.1",
     "@types/multer": "^2.1.0",