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/quota/router.py

@@ -5,6 +5,7 @@
 from fastapi import APIRouter, Depends
 
 from app.core.dependencies import get_current_user
+from app.core.openapi import error_responses
 from app.features.quota.deps import get_quota_service
 from app.features.quota.schemas import QuotaCheckResponse
 from app.features.quota.service import QuotaService
@@ -13,12 +14,7 @@ from app.features.user.models import User
 router = APIRouter(
     prefix="/api/quota",
     tags=["quota"],
-    responses={
-        401: {"description": "认证失败"},
-        403: {"description": "权限不足"},
-        404: {"description": "资源不存在"},
-        429: {"description": "配额已用尽"},
-    },
+    responses=error_responses(401, 403, 404, 429),
 )