Restore the committed embed placeholder index

The built web/dist index.html was committed over the placeholder and
referenced an uncommitted hashed asset. Keep this change limited to CI.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/frontend/dist/index.html

@@ -2,11 +2,10 @@
 <html lang="en">
   <head>
     <meta charset="UTF-8" />
-    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
     <title>MealQuest</title>
-    <script type="module" crossorigin src="/assets/index-B3V1dj9D.js"></script>
   </head>
   <body>
-    <div id="root"></div>
+    <!-- Placeholder so the Go embed compiles. The build replaces this directory with web/dist. -->
+    <p>MealQuest web assets have not been built.</p>
   </body>
 </html>