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/plan/deps.py

@@ -1,13 +1,22 @@
 """Plan feature dependencies: get_plan_service."""
 
+from typing import Annotated
+
 from fastapi import Depends
 
+from app.core.dependencies import get_current_user
 from app.features.plan.service import PlanService
 from app.features.quota.deps import get_quota_service
 from app.features.quota.service import QuotaService
+from app.features.user.models import User
+from app.core.deps_types import DbDep
 
 
 def get_plan_service(
-    quota_service: QuotaService = Depends(get_quota_service),
+    quota_service: Annotated[QuotaService, Depends(get_quota_service)],
 ) -> PlanService:
     return PlanService(quota_service=quota_service)
+
+
+PlanServiceDep = Annotated[PlanService, Depends(get_plan_service)]
+CurrentUserDep = Annotated[User, Depends(get_current_user)]