Done. `petlifeclub/layouts/_default/baseof.html` created with:
- HTML5 structure with `data-theme="light"` and lang="en"
- Skip-to-content link, reading progress bar, back-to-top button
- Partials: head, header, footer
- Inline vanilla JS: reading progress tracking, back-to-top visibility/scroll, header shadow on scroll, mobile menu toggle (nav-open class), theme persistence to localStorage (petlifeclub-theme), copy-link share functionality
- No jQuery, minimal footprint