Fix demo navigation to rely only on URL hash ...

Removed scroll-based active-section detection. Navigation now uses
`hashchange` event and `window.location.hash` exclusively, preventing
cross-tab state leakage.

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

Replace code-example-copy with standard btn-icon ...

All copy buttons inside `.code-example` blocks now use `.btn-icon.btn-icon-sm`
with a Phosphor `ph-copy` icon instead of the old text-based `.code-example-copy`.

Updated `code-examples.js` to swap the icon to `ph-check` for 1.2 s after copy,
matching the behaviour of `GnCopyButton`.

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

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>

Included dist to repo