fix(ui): wrap MQTT buttons on mobile to prevent overflow

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/pages/SettingsPage.tsx

@@ -1658,7 +1658,7 @@ export function SettingsPage() {
               </div>
             )}
 
-            <div className="flex gap-3">
+            <div className="flex flex-wrap gap-3">
               <Button
                 onClick={handleSaveMqttConfig}
                 disabled={isLoading === 'mqtt'}