feat(carousel): add Terms Query block compatibility

[thomasnavarro]

Summary

Adds support for core/terms-query inside carousels. The Terms Query block now works as a content source alongside Query Loop and manual slides, with each term rendered as its own slide.

One catch: Gutenberg's term-template block doesn't add a columns-{N} class to its wrapper (unlike post-template). This PR fixes that server-side (PHP render_block filter) and editor-side (MutationObserver) so the carousel can detect the column count.

Type of change

• Bug fix
• New feature
• Enhancement/refactor
• Documentation update
• Test update
• Build/CI/tooling

Related issue(s)

Closes #97

What changed

• CSS: Added .wp-block-term-template and .wp-block-term selectors alongside existing post-template selectors for flex layout, gap, columns variants, loop mode and vertical axis
• JS (frontend): view.ts detects .wp-block-term-template as Embla container and .wp-block-term as individual slides; useCarouselObservers.ts observes term-template for mutation/resize
• JS (editor): edit.tsx allows core/terms-query in the viewport, reads the term-template's columnCount from the block store, and mirrors the columns-{N} class via MutationObserver (persists across block select/deselect cycles)
• PHP: New render_block_core/term-template filter in Plugin.php adds columns-{N} class to the <ul> wrapper using WP_HTML_Tag_Processor, bridging a parity gap with post-template in Gutenberg core
• Pattern: Rewrote terms-query.php with valid Gutenberg markup — dynamic term-template block (no <ul>/<li> in saved content), carousel-slide wrapper, correct termQuery attributes
• Docs: Added Terms Query to README features/FAQ and USAGE.md setup guide
• Test: Added isSlideActive test for .wp-block-term slide detection

Breaking changes

• Yes
• No

Testing

• Unit tests
• Manual testing
• Cross-browser testing (if UI changes)

Test details:

1. Insert the "Carousel Kit: Terms Query Carousel" pattern in the editor — no "Resolve block" prompt
2. Verify term-template renders correctly with 3 visible terms per slide group
3. Change columnCount in term-template settings (2, 3, 4) — carousel updates in both editor and frontend
4. Select/deselect the term-template block — columns-N class persists on the wrapper
5. Frontend: inspect <ul class="wp-block-term-template columns-3"> — class is present via PHP filter
6. npm run test:js — all tests pass including new Terms Query test

Screenshots / recordings

N/A — to be added during review.

Checklist

• I have self-reviewed this PR
• I have added/updated tests where needed
• I have updated docs where needed
• I have checked for breaking changes

[thomasnavarro]

I'm not 100% sure this is the best approach to work around the missing columns-{N} class on term-template. If anyone has a cleaner implementation in mind, I'm happy to iterate on it.