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/router.py

@@ -2,36 +2,29 @@
 订阅计划路由。
 """
 
-from typing import List
+from fastapi import APIRouter
 
-from fastapi import APIRouter, Depends
-
-from app.core.dependencies import get_current_user
-from app.features.plan.deps import get_plan_service
+from app.core.openapi import error_responses
+from app.features.plan.deps import CurrentUserDep, PlanServiceDep
 from app.features.plan.schemas import CurrentPlanResponse, PlanResponse
-from app.features.plan.service import PlanService, get_plans_for_api
-from app.features.user.models import User
 
 router = APIRouter(
     prefix="/api/plans",
     tags=["plans"],
-    responses={
-        401: {"description": "认证失败"},
-        404: {"description": "资源不存在"},
-    },
+    responses=error_responses(401, 404),
 )
 
 
-@router.get("", response_model=List[PlanResponse])
-async def get_plans():
+@router.get("", response_model=list[PlanResponse])
+def get_plans(service: PlanServiceDep) -> list[PlanResponse]:
     """获取所有可用的订阅计划（开发环境 ENABLE_TEST_PLAN=1 时包含「一分钱测试版」）。"""
-    return get_plans_for_api()
+    return service.get_plans_for_api()
 
 
 @router.get("/current", response_model=CurrentPlanResponse)
 async def get_current_plan(
-    current_user: User = Depends(get_current_user),
-    service: PlanService = Depends(get_plan_service),
-):
+    current_user: CurrentUserDep,
+    service: PlanServiceDep,
+) -> CurrentPlanResponse:
     """获取当前用户的订阅计划信息"""
     return await service.get_current_plan_response(current_user)