chore: match HTML background to Flutter dark theme

Changed from #1a1a2e to #111111 to match FlexScheme.aquaBlue scaffold background.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

web/index.html

@@ -36,7 +36,8 @@
     body {
       margin: 0;
       padding: 0;
-      background-color: #1a1a2e;
+      /* Match Flutter's dark theme scaffold background (FlexScheme.aquaBlue) */
+      background-color: #111111;
     }
   </style>
 </head>