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/src/entities/sync-log.entity.ts

@@ -0,0 +1,35 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn } from 'typeorm';
+
+export type SyncPlatform = 'dingtalk' | 'wecom';
+export type SyncType = 'full' | 'incremental';
+export type SyncStatus = 'running' | 'success' | 'failed';
+
+@Entity('sync_logs')
+export class SyncLog {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column({ type: 'varchar', length: 20 })
+  platform: SyncPlatform;
+
+  @Column({ name: 'sync_type', type: 'varchar', length: 20 })
+  syncType: SyncType;
+
+  @Column({ type: 'varchar', length: 20 })
+  status: SyncStatus;
+
+  @Column({ name: 'records_count', type: 'integer', default: 0 })
+  recordsCount: number;
+
+  @Column({ name: 'error_message', type: 'text', nullable: true })
+  errorMessage: string | null;
+
+  @Column({ name: 'started_at', type: 'datetime', nullable: true })
+  startedAt: Date | null;
+
+  @Column({ name: 'finished_at', type: 'datetime', nullable: true })
+  finishedAt: Date | null;
+
+  @CreateDateColumn({ name: 'created_at' })
+  createdAt: Date;
+}