fix: infinite login loop from async auth validation

- Add _validating flag to prevent recursive hashchange calls during async
  token validation
- route() checks _validating before calling validateAuth(), sets flag
  before async call, clears in .then/.catch handlers
- route() returns early if still validating (waits for completion)
- Fixes: expired token causing infinite login redirect loop

public/js/app.js

@@ -95,13 +95,19 @@ const App = {
   closeModal() { document.getElementById('modal-overlay').classList.add('hidden'); },
   navigate(page, param) { location.hash = `#/${page}` + (param ? `/${param}` : ''); },
 
+  _validating: false,
+
   // 验证 token 有效性(轻量级,失败则清除登录态)
   async validateAuth() {
-    if (!Auth.logged()) return false;
+    if (this._validating) return null; // 防止递归
+    this._validating = true;
+    if (!Auth.logged()) { this._validating = false; return false; }
     try {
       await API.get('/me');
+      this._validating = false;
       return true;
     } catch (e) {
+      this._validating = false;
       if (e && e.message && e.message.includes('登录')) {
         Auth.reset();
         return false;
@@ -126,17 +132,27 @@ const App = {
     if (page === 'login' || page === 'register' || page === 'forgot' || page === 'reset') { this.showPublic(page); return; }
 
     // 访问受保护页面前先验证 token 有效性
-    if (Auth.logged()) {
+    if (Auth.logged() && !this._validating) {
+      this._validating = true; // 标记正在验证
       this.validateAuth().then(valid => {
-        if (!valid) { location.hash = '#/login'; return; }
+        this._validating = false;
+        if (!valid) {
+          location.hash = '#/login';
+          return;
+        }
         this._doRoute(page, param);
       }).catch(() => {
+        this._validating = false;
         Auth.reset();
         location.hash = '#/login';
       });
       return;
     }
+    if (!Auth.logged()) {
       location.hash = '#/login';
+      return;
+    }
+    // 正在验证中,不做任何操作(等待验证完成)
   },
 
   _doRoute(page, param) {