零 Node 部署、超级管理员，并完善本地构建发布文档。

- FastAPI 单进程托管 frontend/dist，systemd 替代 PM2

- 超级管理员 admin、注册开关与用户管理

- README/DEPLOY/USAGE 说明：改代码须本地构建 dist 后 push，服务器 update.sh

- 提交 frontend/dist 与 build-frontend 脚本

backend/app/routers/auth.py

@@ -13,14 +13,27 @@ from app.core.security import (
     get_password_hash,
     verify_password,
 )
-from app.models.user import User
+from app.models.user import SystemSettings, User
 from app.schemas import RefreshRequest, TokenResponse, UserLogin, UserOut, UserRegister
 
 router = APIRouter(prefix="/auth", tags=["auth"])
 
 
+def get_or_create_settings(db: Session) -> SystemSettings:
+    row = db.get(SystemSettings, 1)
+    if row is None:
+        row = SystemSettings(id=1, registration_enabled=True)
+        db.add(row)
+        db.commit()
+        db.refresh(row)
+    return row
+
+
 @router.post("/register", response_model=UserOut, status_code=status.HTTP_201_CREATED)
 def register(data: UserRegister, db: Session = Depends(get_db)):
+    settings_row = get_or_create_settings(db)
+    if not settings_row.registration_enabled:
+        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail="注册已关闭，请联系管理员")
     if db.query(User).filter(User.username == data.username).first():
         raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST, detail="用户名已存在")
     user = User(username=data.username, password_hash=get_password_hash(data.password))