Update: Drop WOFF2 icon font (fixes #877)

[swashbuck]

Fixes #877

Update

• Removed the WOFF2 icon font. IcoMoon's free plan no longer generates WOFF2, so the file could not be kept in step with future icon-set changes. The @font-face rule now loads WOFF only, which every supported browser handles.
• Updated the fonts README.md so the regeneration steps no longer ask for a WOFF2 export, and noted why one should not be added back.

Performance Impact

The icon font download grows from 18.5KB to 31KB. It is a single request, cached after first load, so the effect is negligible.

Testing

1. Build a course and load it in a browser.
2. Confirm all icons render as before (navigation bar, drawer, buttons, accordion/narrative controls).
3. Check the network panel: only vanilla.woff is requested, and there is no 404 for vanilla.woff2.

Posted via collaboration with Claude Code

[kirsty-hames]

Works as expected thanks @swashbuck 👍 Testing across Safari, Firefox and Chrome on macOS