新增前后端AI聊天模块，包括流式对话、配置管理和UI组件优化。

backend/app/main.py

@@ -0,0 +1,37 @@
+from contextlib import asynccontextmanager
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from .database import init_db
+from .routers.novels import router as novels_router
+from .routers.outlines import router as outlines_router
+from .routers.ai_config import router as ai_config_router
+from .routers.chat import router as chat_router
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    init_db()
+    yield
+
+
+app = FastAPI(title="Noval", version="0.1.0", lifespan=lifespan)
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=["http://localhost:5173"],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(novels_router)
+app.include_router(outlines_router)
+app.include_router(ai_config_router)
+app.include_router(chat_router)
+
+
+@app.get("/api/health")
+def health():
+    return {"status": "ok"}