fix: stop excluding GIF from Jekyll build

The claude-rewind.gif was excluded by _config.yml, causing a 404
on GitHub Pages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: css521

docs/_config.yml

@@ -10,5 +10,5 @@ kramdown:
 exclude:
   - openapi.json
   - "*.cast"
-  - "*.gif"
   - README.md
+  - Gemfile.lock