三端自适应布局与 PWA 可安装支持

新增响应式样式、手机侧滑导航、manifest 与 Service Worker；补充根路径重定向与安装 App 入口。

Co-authored-by: Cursor <cursoragent@cursor.com>

app.py

@@ -551,6 +551,28 @@ def login_required(f):
     return wrap
 
 
+@app.route("/")
+def index():
+    if session.get("logged_in"):
+        return redirect(url_for("plans"))
+    return redirect(url_for("login"))
+
+
+@app.route("/manifest.webmanifest")
+def web_manifest():
+    response = app.send_static_file("manifest.json")
+    response.mimetype = "application/manifest+json"
+    return response
+
+
+@app.route("/sw.js")
+def service_worker():
+    response = app.send_static_file("sw.js")
+    response.headers["Cache-Control"] = "no-cache"
+    response.headers["Service-Worker-Allowed"] = "/"
+    return response
+
+
 @app.route("/login", methods=["GET", "POST"])
 def login():
     if request.method == "POST":