Fix v0.4.0 review findings and demo asset paths ...

- Restore visible hover feedback on radio/checkbox (background $color-grey)
- Drop dead checked/hover border-color rules; guard checked with :not(:disabled)
- Tokenize radio border as $border-width-choice and add $range-thumb-size
  so the choice-size bump no longer widens range slider thumbs
- Add cursor: pointer to switch wrapper
- Revert escaped doc snippets to absolute URLs (relative sweep was
  teaching fake ./routes in documentation samples)
- Add compare-heights.js demo sync check with CHROME_PATH fallback;
  ignore screenshots/

v0.4.0 — GnRepeater, redesigned checkbox/radio ...

- Add GnRepeater Vue component for dynamic field groups
- Redesign checkbox and radio styles to match kit aesthetic:
  hard-panel background, accent borders, checkmark/dot indicators,
  hover → primary border, checked → subtle tint + colored mark
- Bump version to 0.4.0

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Replace translucent $surface-panel-muted with solid $color-dark ...

$surface-panel-muted was `rgba($color-text-light, 0.045)` — an ugly,
almost-invisible blue tint. It is now `=#1F2335`, the proper dark panel
background for cards, groups, tables, tabs, drawers, etc.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Modernize Sass build pipeline

Add Tokyo Night color pass

Scaffold GNexus UI kit