fix: remove HTTPAuthCredentials import (FastAPI compatibility)

backend/auth.py

@@ -6,7 +6,7 @@ import os
 from datetime import datetime, timedelta, timezone
 from typing import Optional
 from fastapi import Depends, HTTPException, status
-from fastapi.security import HTTPBearer, HTTPAuthCredentials
+from fastapi.security import HTTPBearer
 from jose import JWTError, jwt
 from pydantic import BaseModel
 
@@ -58,7 +58,7 @@ def create_access_token(user_id: int, username: str, role: str, expires_delta: O
     return encoded_jwt
 
 
-async def get_current_user(credentials: HTTPAuthCredentials = Depends(security)):
+async def get_current_user(credentials = Depends(security)):
     """
     Dependency that validates JWT token from Authorization header.
     Returns TokenData with user_id, username, role.