施工(HEL-226): 实现登录门户与本机免密切换账号

用设备 Cookie 和授权表记住本机已验证账号，登录页按确认样图做成门户，不再把密码写进浏览器。

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: multica-agent <github@multica.ai>

frontend/app.js

@@ -25,8 +25,10 @@ async function initialize() {
   try {
     const session = await apiRequest("/api/auth/me");
     if (!session.authenticated) {
-      if (session.registration_required) selectAuthMode("register");
-      showAuthGate();
+      const params = new URLSearchParams();
+      if (session.registration_required) params.set("mode", "register");
+      const query = params.toString();
+      window.location.replace("/login/" + (query ? `?${query}` : ""));
       return;
     }
     await applyAuthenticatedSession(session);