refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/app/features/payment/deps.py

@@ -1,12 +1,11 @@
 from fastapi import Depends
-from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.core.db import get_async_db
 from app.features.payment.order_service import PaymentOrderService
 from app.features.payment.payment_config import PaymentConfig
 from app.features.payment.payment_facade import PaymentService
 from app.features.plan.deps import get_plan_service
 from app.features.plan.service import PlanService
+from app.core.deps_types import DbDep
 
 _payment_service = None
 
@@ -21,7 +20,7 @@ def get_payment_service() -> PaymentService:
 
 
 def get_payment_order_service(
-    db: AsyncSession = Depends(get_async_db),
+    db: DbDep,
     plan_service: PlanService = Depends(get_plan_service),
 ) -> PaymentOrderService:
     """Payment order facade: create_order, callbacks, list/status."""