refactor(park-desktop): admin 后台新 UI + vision_yolo 手势接入，清理设计文档与安装包，补充工作区规范

backend/app/main.py

@@ -14,7 +14,7 @@ from pathlib import Path
 
 from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
-from fastapi.responses import FileResponse, JSONResponse
+from fastapi.responses import FileResponse, JSONResponse, RedirectResponse
 from fastapi.staticfiles import StaticFiles
 from pydantic import BaseModel
 
@@ -171,17 +171,7 @@ async def update_check(body: UpdateCheckBody):
 # ---------- 前端静态托管 + SPA 回退（浏览器直接访问 :8000 即可） ----------
 
 @app.get("/{path:path}", include_in_schema=False)
-async def spa_fallback(path: str):
-    if not DIST.exists():
-        return JSONResponse({"detail": "前端未构建（dist 目录不存在）"}, status_code=404)
-    dist = DIST.resolve()
-    if not path:
-        target = dist / "index.html"
-    else:
-        target = (dist / path).resolve()
-    if target.is_file() and target.is_relative_to(dist):
-        return FileResponse(target)
-    index = dist / "index.html"
-    if index.exists():
-        return FileResponse(index)
-    return JSONResponse({"detail": "Not Found"}, status_code=404)
+async def spa_fallback(request: Request):
+    """默认导向管理后台：屏蔽通过后端地址直接访问大屏前端（含首页 / 及 /twin /ai /screen 等）。
+       /api、/admin、/static、/file 等已在更早路由/挂载处理，不会走到这里。"""
+    return RedirectResponse(url="/admin", status_code=307)