fix(worker): 初始化 PostgreSQL 連線池 - 修復 Incident DB 持久化

問題:
- Signal Worker 沒有初始化 PostgreSQL，導致 incidents 表可能不存在
- Incident 只寫入 Redis，未持久化到 PostgreSQL
- 審核後無法正確更新 DB 狀態

修復:
- 在 Signal Worker 啟動時呼叫 init_db() 建立表
- 在關閉時呼叫 close_db() 釋放連線池
- 增加 PostgreSQL 初始化日誌

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/workers/signal_worker.py

@@ -326,17 +326,30 @@ async def _main() -> None:
     # Initialize settings first (loads env vars)
     from src.core.config import settings  # noqa: F401
     from src.core.redis_client import init_redis_pool, close_redis_pool, init_worker_redis_pool, close_worker_redis_pool
+    from src.db.base import init_db, close_db
 
     logger.info(
         "signal_worker_standalone_starting",
         environment=settings.ENVIRONMENT,
         redis_url=settings.REDIS_URL.split("@")[-1] if settings.REDIS_URL else "N/A",
+        database_url=settings.DATABASE_URL.split("@")[-1] if settings.DATABASE_URL else "N/A",
     )
 
     # Initialize Redis (API pool + Worker 專屬長連線池)
     await init_redis_pool()
     await init_worker_redis_pool()  # Worker 專屬，無超時限制
 
+    # Initialize PostgreSQL (Episodic Memory) - 確保 incidents 表存在
+    try:
+        await init_db()
+        logger.info("postgresql_initialized", status="ok")
+    except Exception as e:
+        logger.error(
+            "postgresql_init_failed",
+            error=str(e),
+            message="Episodic Memory (DB) will be unavailable - incidents won't persist",
+        )
+
     # Write health files for K8s probes
     await _write_health_files()
 
@@ -361,6 +374,7 @@ async def _main() -> None:
     await worker.stop()
     await close_worker_redis_pool()  # 關閉 Worker 專屬連線
     await close_redis_pool()
+    await close_db()  # 關閉 PostgreSQL 連線池
 
     # Remove health files
     from pathlib import Path