Add FastAPI backend with agent system

backend/app/main.py

@@ -0,0 +1,72 @@
+from contextlib import asynccontextmanager
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+from app.database import init_db
+from app.routers import (
+    auth_router,
+    conversation_router,
+    document_router,
+    task_router,
+    forum_router,
+    graph_router,
+    agent_router,
+    todo_router,
+    settings_router,
+    folder_router,
+)
+from app.routers.scheduler import router as scheduler_router
+from app.services.scheduler_service import start_scheduler, stop_scheduler, get_scheduler_status
+from app.config import settings
+import os
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # 启动
+    os.makedirs(settings.DATA_DIR, exist_ok=True)
+    os.makedirs(settings.UPLOAD_DIR, exist_ok=True)
+    os.makedirs(settings.CHROMA_PERSIST_DIR, exist_ok=True)
+    await init_db()
+    start_scheduler()
+    yield
+    # 关闭
+    stop_scheduler()
+
+
+app = FastAPI(
+    title=settings.APP_NAME,
+    version=settings.APP_VERSION,
+    lifespan=lifespan,
+)
+
+# CORS
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=settings.CORS_ORIGINS,
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+# 注册路由
+app.include_router(auth_router)
+app.include_router(conversation_router)
+app.include_router(document_router)
+app.include_router(task_router)
+app.include_router(forum_router)
+app.include_router(graph_router)
+app.include_router(agent_router)
+app.include_router(todo_router)
+app.include_router(settings_router)
+app.include_router(folder_router)
+app.include_router(scheduler_router)
+
+
+@app.get("/api/health")
+async def health():
+    return {
+        "status": "ok",
+        "version": settings.APP_VERSION,
+        "llm_provider": settings.LLM_PROVIDER,
+        "scheduler": get_scheduler_status(),
+    }