🎉 Initial commit: QQuiz - 智能刷题与题库管理平台

## 功能特性

✅ **核心功能**
- 多文件上传与智能去重（基于 content_hash）
- 异步文档解析（支持 TXT/PDF/DOCX/XLSX）
- AI 智能题目提取与评分（OpenAI/Anthropic/Qwen）
- 断点续做与进度管理
- 自动错题本收集

✅ **技术栈**
- Backend: FastAPI + SQLAlchemy 2.0 + PostgreSQL
- Frontend: React 18 + Vite + Tailwind CSS
- Deployment: Docker Compose

✅ **项目结构**
- 53 个文件
- 完整的前后端分离架构
- Docker/源码双模部署支持

🚀 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/services/auth_service.py

@@ -0,0 +1,78 @@
+"""
+Authentication Service
+"""
+from fastapi import Depends, HTTPException, status
+from fastapi.security import HTTPBearer, HTTPAuthorizationCredentials
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy import select
+from typing import Optional
+
+from models import User
+from database import get_db
+from utils import decode_access_token
+
+security = HTTPBearer()
+
+
+async def get_current_user(
+    credentials: HTTPAuthorizationCredentials = Depends(security),
+    db: AsyncSession = Depends(get_db)
+) -> User:
+    """
+    Get current authenticated user from JWT token.
+    """
+    token = credentials.credentials
+    credentials_exception = HTTPException(
+        status_code=status.HTTP_401_UNAUTHORIZED,
+        detail="Could not validate credentials",
+        headers={"WWW-Authenticate": "Bearer"},
+    )
+
+    # Decode token
+    payload = decode_access_token(token)
+    if payload is None:
+        raise credentials_exception
+
+    user_id: int = payload.get("sub")
+    if user_id is None:
+        raise credentials_exception
+
+    # Get user from database
+    result = await db.execute(select(User).where(User.id == user_id))
+    user = result.scalar_one_or_none()
+
+    if user is None:
+        raise credentials_exception
+
+    return user
+
+
+async def get_current_admin_user(
+    current_user: User = Depends(get_current_user)
+) -> User:
+    """
+    Get current user and verify admin permissions.
+    """
+    if not current_user.is_admin:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Not enough permissions"
+        )
+    return current_user
+
+
+async def get_optional_user(
+    credentials: Optional[HTTPAuthorizationCredentials] = Depends(security),
+    db: AsyncSession = Depends(get_db)
+) -> Optional[User]:
+    """
+    Get current user if token is provided, otherwise return None.
+    Useful for endpoints that work for both authenticated and anonymous users.
+    """
+    if credentials is None:
+        return None
+
+    try:
+        return await get_current_user(credentials, db)
+    except HTTPException:
+        return None