fix: copy collection static files to Jekyll output

[tallnato]

Summary

• Adds a Jekyll generator plugin (_plugins/copy_collection_files.rb) that copies non-document static files (.mp3, .wav, .fseq, .png, etc.) from _-prefixed collection directories into the _site/ output at the correct content/{collection}/{slug}/ paths
• Adds type attribute to <source> elements in _layouts/item.html for better browser audio compatibility (mp3→audio/mpeg, wav→audio/wav, ogg→audio/ogg)

Why

Jekyll processes collection documents (Markdown) into HTML pages but does not automatically copy static files from _-prefixed collection directories to the build output. Audio files, thumbnails, and downloadable files were missing from the deployed site, breaking <audio> playback and download links.

How to verify

1. npm install && npm run build && bundle exec jekyll build
2. Confirm static files exist in _site/content/:
   • _site/content/boombox/sample-track/sample-track.mp3
   • _site/content/locksounds/sample-chime/sample-chime.wav
   • _site/content/lightshows/sample-show/sample-show.fseq
   • _site/content/wraps/sample-wrap/sample-wrap.png
3. Check <source> elements include type attributes in generated HTML
4. Works both locally (bundle exec jekyll serve) and in the deploy workflow

Test plan

• Local jekyll build succeeds with all static files in _site/content/
• Audio <source> elements include correct type attributes
• Download links point to files that exist in build output
• CI checks pass
• Deploy workflow produces correct output

🤖 Generated with Claude Code

[tallnato]

Code Review (Revinaldo)

No issues found. Checked for bugs and CLAUDE.md compliance.

• _plugins/copy_collection_files.rb — correctly copies static files from _-prefixed collection dirs to _site/ output. Path construction, Pathname usage, and Dir.glob filtering are all sound.
• _layouts/item.html — MIME type detection via Liquid is correct; type attribute is conditionally added only for known formats (mp3, wav, ogg).

LGTM — good to merge.