ui: guard meta count against null tunnels list

/api/tunnels returns {"tunnels": null} when no bridges are active.
The previous code path short-circuited the empty render but still
dereferenced j.tunnels.length on the line that updates the header
meta — TypeError, then the "— connecting…" placeholder stuck around
forever. Coalesce to [] before .length.

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

internal/httpsrv/static/index.html

@@ -118,7 +118,7 @@ async function refreshConnections() {
         rows.appendChild(tr);
       }
     }
-    document.getElementById('meta').textContent = '— ' + j.tunnels.length + ' tunnels';
+    document.getElementById('meta').textContent = '— ' + ((j.tunnels || []).length) + ' tunnels';
   } catch (e) {
     document.getElementById('meta').textContent = '— api error';
   }