fix(api): cap db pool during prod rollout

apps/api/src/core/config.py

@@ -273,6 +273,24 @@ class Settings(BaseSettings):
     DATABASE_URL: str = Field(
         description="PostgreSQL connection URL (必填，從 K8s Secret awoooi-secrets → DATABASE_URL 取得)",
     )
+    DATABASE_POOL_SIZE: int = Field(
+        default=1,
+        ge=1,
+        le=10,
+        description="SQLAlchemy asyncpg pool size. Production DB role currently has a very small connection budget.",
+    )
+    DATABASE_MAX_OVERFLOW: int = Field(
+        default=0,
+        ge=0,
+        le=20,
+        description="Extra asyncpg connections above DATABASE_POOL_SIZE. Keep 0 in production until DB role limit is raised.",
+    )
+    DATABASE_POOL_TIMEOUT_SECONDS: float = Field(
+        default=5.0,
+        ge=1.0,
+        le=30.0,
+        description="Seconds to wait for a pooled DB connection before failing visible.",
+    )
 
     # ==========================================================================
     # Redis (192.168.0.188:6380, DB 0 - 與 OpenClaw 共用)