Ensure every icon carries the base `ph` class ...

- `iconNode()` in `src/vue/utils.js` now always prepends `ph` to the
  generated <i> class list, guaranteeing the base Phosphor font-family.
- Fix all raw HTML/JS spinners that used `ph-bold ph-spinner` without
  the base `ph` class: buttons demo, helper.js loading states.

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

Add GnCopyButton component and strict icon rule in docs ...

- Create GnCopyButton Vue adapter component with clipboard copy
  and 3-second icon swap from ph-copy to ph-check.
- Register GnCopyButton in plugin and index exports.
- Add copy-button demo block to demo/partials/buttons.html.
- Update CLAUDE.md, README, and Vue docs with component entry.
- Enforce "all icons must carry the ph class" rule in CLAUDE.md.

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

Scaffold GNexus UI kit