后台同步异常时前端显示错误提示，不再卡住页面

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ft-app/app/templates/admin.html

@@ -192,6 +192,12 @@
 </div>
 
 <script>
+function escapeHtml(s) {
+  var d = document.createElement('div');
+  d.appendChild(document.createTextNode(s));
+  return d.innerHTML;
+}
+
 var syncTimer = null;
 var progressShownAt = 0;
 
@@ -218,6 +224,19 @@ function pollProgress() {
       document.getElementById('sync-progress-pct').textContent = pct + '%';
       document.getElementById('sync-progress-label').textContent = data.label;
 
+      if (data.error) {
+        clearInterval(syncTimer);
+        syncTimer = null;
+        document.getElementById('sync-progress-bar').style.background = 'var(--danger)';
+        document.getElementById('sync-progress-label').innerHTML =
+          '<span style="color:var(--danger-fg);">✕ ' + escapeHtml(data.label) + '</span>' +
+          '<span style="display:block;font-size:0.78rem;color:var(--danger-fg);margin-top:4px;">' + escapeHtml(data.error) + '</span>';
+        document.getElementById('sync-progress-pct').textContent = '';
+        document.getElementById('sync-progress').insertAdjacentHTML('beforeend',
+          '<button onclick="hideProgress()" style="display:block;margin-top:10px;padding:4px 14px;border:1px solid var(--border);border-radius:5px;background:var(--surface);color:var(--fg);cursor:pointer;font-size:0.8rem;">关闭</button>');
+        return;
+      }
+
       if (data.finished) {
         var elapsed = Date.now() - progressShownAt;
         var delay = elapsed < 1000 ? 1000 - elapsed : 0;