Add HTML fallback and improve bubble rendering in collapsed tool calls

- Create image_html.php as fallback when GD not available
- Add test.html page to demonstrate different bubble styles
- Update index.js to support rendering bubbles in collapsed tool calls
- Improve example.html settings page with new options
- Add reference/ to .gitignore

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

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

.gitignore

@@ -4,6 +4,9 @@ mounts/
 # Ignore fonts directory
 fonts/
 
+# Ignore reference repos
+reference/
+
 # Node modules
 node_modules/