refactor(auth): remove legacy RESTful user routes and migrate authentication to GraphQL context

- Rename get_current_user to get_current_user_id in auth/deps.py to clarify intent
- Remove legacy /me, /logout routes, and placeholder function from auth/__init__.py
- Remove dependency_overrides from app/main.py
- Update CustomContext to resolve and cache full User objects via db query

app/graphql/context.py

@@ -1,9 +1,9 @@
 from app.models.user import User
-from auth.deps import get_current_user
+from auth.deps import get_current_user_id
 from fastapi import Request
 from strawberry.fastapi import BaseContext
 from strawberry.dataloader import DataLoader
-from typing import List
+from typing import List, Optional
 from collections import defaultdict
 from app.db import SessionLocal
 from app.models import WorkspaceMember
@@ -31,13 +31,22 @@ class CustomContext(BaseContext):
         super().__init__(request)
         self.db = SessionLocal()
         self.request = request
+        self._current_user: Optional[User] = None
         
         self.members_loader = DataLoader(load_fn=load_members_by_workspace_ids)
 
     async def get_current_user(self) -> User | None:
-        # 复用现有的 auth 逻辑
+        """在 Context 级别负责把 user_id 变成真正的数据库 User 对象"""
+        if self._current_user is not None:
+            return self._current_user
+            
         try:
-            return await get_current_user(self.request)
+            # 借用 auth 包的纯工具解出 ID
+            user_id = get_current_user_id(self.request)
+            # 在 Context 的数据库连接中查询完整用户
+            user = self.db.query(User).filter(User.id == user_id).first()
+            self._current_user = user
+            return user
         except Exception:
             return None