feat(theme): add id attribute to group/category section headings

[Metbcy]

Closes #3029.

Summary

Adds an id attribute to the <h2> group/category section headings rendered by the default theme's members and moduleReflection partials so that section headers can be linked to directly via fragment URLs (e.g. …/MyClass.html#methods).

Changes

• src/lib/output/themes/default/partials/members.tsx — slug section.title via context.slugger.slug(...) and pass it to the heading <h2> as id.
• src/lib/output/themes/default/partials/moduleReflection.tsx — same treatment for the module-reflection sections (skipped for the unnamed/none section, which has no title to slug).
• CHANGELOG.md — Unreleased note under Features.
• Snapshot specs regenerated with pnpm rebuild_specs (only the new id attribute is added to the h2 tag — no other changes).

The slugger is the existing per-page Slugger instance, which already tracks heading collisions for member anchors, so section anchors will be deduplicated against everything else on the page automatically.

Testing

• pnpm lint — clean.
• pnpm build — clean.
• pnpm test — 1046 passing.
• pnpm rebuild_specs — snapshot diff is exclusively the new id attributes.

[Gerrit0]

Thank you! This is a good start, however these ID attributes are only usable if someone goes and figures out what they'll be with developer tools. We should also add an index link like #3072 did, before becoming abandoned.

[Metbcy]

Thanks for the review @Gerrit0! Pushed dfab33f to address the feedback:

• Added the visible anchor icon + tsd-anchor-link class to the section <h2> in members.tsx and moduleReflection.tsx, mirroring feat(theme): add id attributes to group headings for linking #3072.
• Extended the same treatment to the <h3> section headings in index.tsx so the in-page index entries are also linkable. None sections remain unanchored.
• The per-page slugger naturally disambiguates collisions between the index entry and the later member section (e.g. #methods on the index, #methods-1 on the heading).

Snapshots regenerated; full test suite (1046) + lint pass locally. Let me know if you'd like the index/members slugs swapped (members getting the bare slug, index the -1 suffix) or any other tweak.

[Gerrit0]

My apologies for the delay here, life has been busy.

The anchors do not seem to display correctly now within the page:

Otherwise, this looks good to me

[Metbcy]

My apologies for the delay here, life has been busy.

The anchors do not seem to display correctly now within the page:

Otherwise, this looks good to me

No worries man, life gets busy. Let me dig in and see if I can fix the anchoring.

[Metbcy]

Fixed in 21159e7. Root cause was a stale rule in static/style.css:

.tsd-accordion-summary a { width: calc(100% - 1.5rem); }

That was written for the nav accordion's direct-child <a>, but the descendant selector also matched the new <a.tsd-anchor-icon> nested inside the <h2> in section summaries, stretching it to fill the row and wrapping it to a second line.

Tightened to a direct-child combinator (.tsd-accordion-summary > a) so the nav case is unaffected and the anchor icon falls back to its normal .tsd-anchor-icon styling (inline-flex, 1em SVG, hidden until hover).

Anchor <a> is now 24px wide (was 163px), heading 28.8px tall (was 57.6px, wrapped). 1046 tests passing.

[Gerrit0]

Thanks!