🎉 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/database.py

@@ -0,0 +1,132 @@
+"""
+Database configuration and session management
+"""
+from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker
+from sqlalchemy.pool import NullPool
+from contextlib import asynccontextmanager
+from typing import AsyncGenerator
+import os
+from dotenv import load_dotenv
+
+# Load environment variables
+load_dotenv()
+
+# Get database URL from environment
+DATABASE_URL = os.getenv("DATABASE_URL")
+
+if not DATABASE_URL:
+    raise ValueError("DATABASE_URL environment variable is not set")
+
+# Create async engine
+engine = create_async_engine(
+    DATABASE_URL,
+    echo=False,  # Set to True for SQL query logging during development
+    future=True,
+    poolclass=NullPool if "sqlite" in DATABASE_URL else None,
+)
+
+# Create async session factory
+AsyncSessionLocal = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,
+    autocommit=False,
+    autoflush=False,
+)
+
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    """
+    Dependency for getting async database session.
+
+    Usage in FastAPI:
+        @app.get("/items")
+        async def get_items(db: AsyncSession = Depends(get_db)):
+            ...
+    """
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()
+
+
+async def init_db():
+    """
+    Initialize database tables.
+    Should be called during application startup.
+    """
+    from models import Base
+
+    async with engine.begin() as conn:
+        # Create all tables
+        await conn.run_sync(Base.metadata.create_all)
+        print("✅ Database tables created successfully")
+
+
+async def init_default_config(db: AsyncSession):
+    """
+    Initialize default system configurations if not exists.
+    """
+    from models import SystemConfig, User
+    from sqlalchemy import select
+    from passlib.context import CryptContext
+
+    pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
+
+    # Default configurations
+    default_configs = {
+        "allow_registration": os.getenv("ALLOW_REGISTRATION", "true"),
+        "max_upload_size_mb": os.getenv("MAX_UPLOAD_SIZE_MB", "10"),
+        "max_daily_uploads": os.getenv("MAX_DAILY_UPLOADS", "20"),
+        "ai_provider": os.getenv("AI_PROVIDER", "openai"),
+    }
+
+    for key, value in default_configs.items():
+        result = await db.execute(select(SystemConfig).where(SystemConfig.key == key))
+        existing = result.scalar_one_or_none()
+
+        if not existing:
+            config = SystemConfig(key=key, value=str(value))
+            db.add(config)
+            print(f"✅ Created default config: {key} = {value}")
+
+    # Create default admin user if not exists
+    result = await db.execute(select(User).where(User.username == "admin"))
+    admin = result.scalar_one_or_none()
+
+    if not admin:
+        admin_user = User(
+            username="admin",
+            hashed_password=pwd_context.hash("admin123"),  # Change this password!
+            is_admin=True
+        )
+        db.add(admin_user)
+        print("✅ Created default admin user (username: admin, password: admin123)")
+        print("⚠️  IMPORTANT: Please change the admin password immediately!")
+
+    await db.commit()
+
+
+@asynccontextmanager
+async def get_db_context():
+    """
+    Context manager for getting database session outside of FastAPI dependency injection.
+
+    Usage:
+        async with get_db_context() as db:
+            result = await db.execute(...)
+    """
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()