feat: add public question bank sync worker

.env.example

@@ -67,6 +67,12 @@ WORKER_ASSET_MIN_AGE_SECONDS=300
 WORKER_ASSET_RECHECK_INTERVAL_SECONDS=86400
 WORKER_ASSET_REQUEST_TIMEOUT_MS=10000
 
+# Worker 配置：公共题库自动同步。冲突会保留租户自改题目并等待后台处理。
+WORKER_PUBLIC_BANK_SYNC_BATCH_SIZE=5
+WORKER_PUBLIC_BANK_SYNC_COPY_LIMIT=1000
+WORKER_PUBLIC_BANK_SYNC_ID=public-banks-1
+WORKER_PUBLIC_BANK_SYNC_CLAIM_STALE_SECONDS=900
+
 # 对象存储配置：API 和 assets worker 共用
 STORAGE_DEFAULT_PROVIDER=local_dev
 STORAGE_DEFAULT_BUCKET=tenant-assets