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/user/service.py

@@ -3,7 +3,8 @@ from datetime import timedelta
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.cos_url_keys import avatar_url_for_api_response
-from app.core.db import utc_now
+from app.core.db import transactional, utc_now
+from app.core.errors import BadRequestError, NotFoundError
 from app.core.logging import get_logger
 from app.core.redis import redis_service
 from app.core.task_tracker import task_tracker
@@ -50,16 +51,19 @@ class UserService:
     def __init__(self, db: AsyncSession):
         self._db = db
 
+    async def get_by_id(self, user_id: str) -> User | None:
+        return await repo.get_user_by_id(user_id, self._db)
+
     async def update_profile(
         self, user_id: str, body: UpdateUserProfileRequest
     ) -> UserProfileResponse:
         user = await repo.get_user_by_id(user_id, self._db)
         if not user:
-            raise ValueError("用户不存在")
-        for field in ("birth_year", "birth_place", "grew_up_place", "occupation"):
-            if field in body.model_fields_set:
-                setattr(user, field, getattr(body, field))
-        await self._db.commit()
+            raise NotFoundError("用户不存在")
+        async with transactional(self._db):
+            for field in ("birth_year", "birth_place", "grew_up_place", "occupation"):
+                if field in body.model_fields_set:
+                    setattr(user, field, getattr(body, field))
         await self._db.refresh(user)
         return _user_to_profile(user)
 
@@ -68,24 +72,23 @@ class UserService:
     ) -> TestSubscriptionResponse:
         user = await repo.get_user_by_id(user_id, self._db)
         if not user:
-            raise ValueError("用户不存在")
+            raise NotFoundError("用户不存在")
         now = utc_now()
-        if action == "activate":
-            user.subscription_type = plan_id
-            user.subscription_expires_at = now + timedelta(days=365)
-            await self._db.commit()
-            return TestSubscriptionResponse(
-                success=True,
-                message=f"已开启测试订阅：{plan_id}",
-                subscription_type=plan_id,
-            )
-        user.subscription_type = "free"
-        user.subscription_expires_at = None
-        await self._db.commit()
+        async with transactional(self._db):
+            if action == "activate":
+                user.subscription_type = plan_id
+                user.subscription_expires_at = now + timedelta(days=365)
+                subscription_type = plan_id
+                message = f"已开启测试订阅：{plan_id}"
+            else:
+                user.subscription_type = "free"
+                user.subscription_expires_at = None
+                subscription_type = "free"
+                message = "已关闭测试订阅，恢复免费体验版"
         return TestSubscriptionResponse(
             success=True,
-            message="已关闭测试订阅，恢复免费体验版",
-            subscription_type="free",
+            message=message,
+            subscription_type=subscription_type,
         )
 
     async def purge_all_user_data(
@@ -97,11 +100,11 @@ class UserService:
     ) -> PurgeUserDataResponse:
         """物理删除该用户业务数据（保留 users 行与登录字段）；并清空出生年/出生地等档案字段；提交后再清 Redis 等。"""
         if confirmation != PURGE_USER_DATA_CONFIRMATION:
-            raise ValueError("确认文案不正确，请按提示完整输入口令")
+            raise BadRequestError("确认文案不正确，请按提示完整输入口令")
 
         user = await repo.get_user_by_id(user_id, self._db)
         if not user:
-            raise ValueError("用户不存在")
+            raise NotFoundError("用户不存在")
 
         logger.info("用户数据清空开始 user_id={}", user_id)
 
@@ -120,10 +123,10 @@ class UserService:
             len(story_ids),
         )
 
-        await repo.purge_user_related_rows(self._db, user_id)
-        await repo.clear_user_demographics(self._db, user_id)
-        await repo.clear_user_avatar_url(self._db, user_id)
-        await self._db.commit()
+        async with transactional(self._db):
+            await repo.purge_user_related_rows(self._db, user_id)
+            await repo.clear_user_demographics(self._db, user_id)
+            await repo.clear_user_avatar_url(self._db, user_id)
         logger.info("用户数据 DB 行已删除、档案字段已清空并提交 user_id={}", user_id)
 
         if object_storage and storage_keys: