fix(settings): re-render panel when last engine unchecked to enforce minimum

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/views/static/js/settings.js

@@ -161,6 +161,10 @@ function renderPanel(prefs) {
       } else {
         newPrefs.engines = newPrefs.engines.filter(function(e) { return e !== cb.value; });
       }
+      if (newPrefs.engines.length === 0) {
+        renderPanel(loadPrefs());
+        return;
+      }
       savePrefs(newPrefs);
       syncEngineInput(newPrefs);
     });