Add admonition styling to odoc CSS and cleanup deprecated/dune
- Add CSS styles for @admonition.note, @admonition.warning,
@admonition.tip, and @admonition.important tags
- Styles include colored backgrounds and left borders:
- Note: blue (#2196F3)
- Warning: orange (#FF9800)
- Tip: green (#4CAF50)
- Important: red (#F44336)
- Remove redundant install stanza from deprecated/dune since the
parent doc/dune now handles these files via glob_files
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>