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>

example.html

@@ -16,8 +16,8 @@
             </div>
 
             <div class="sillybubble_block flex-container">
-                <label for="sillybubble_image_url">Image Service URL:</label>
-                <input id="sillybubble_image_url" type="text" class="text_pole" />
+                <label for="sillybubble_image_url">Image Service URL (full URL including https://):</label>
+                <input id="sillybubble_image_url" type="text" class="text_pole" placeholder="https://calista.the.sexiest.cat/image.php" />
             </div>
 
             <div class="sillybubble_block flex-container">