fix: Make MCP App UIs responsive for narrow viewports (#135)

Changed from min-width: 425px to:
- width: 100%
- max-width: 425px
- box-sizing: border-box

This allows the apps to shrink on narrow viewports (like mobile
or when embedded in native WebViews) instead of causing horizontal
scrolling.

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

Co-authored-by: Claude <noreply@anthropic.com>

examples/basic-server-react/src/mcp-app.module.css

@@ -3,7 +3,9 @@
   --color-primary-hover: #1d4ed8;
   --color-notice-bg: #eff6ff;
 
-  min-width: 425px;
+  width: 100%;
+  max-width: 425px;
+  box-sizing: border-box;
 
   > * {
     margin-top: 0;