fix(core): restrict focusableSelector href matching to real links

[bhamodi]

Summary

FOCUSABLE_SELECTOR (packages/core/src/hooks/focusableSelector.ts:25) built the canonical focusable-elements selector with a bare [href] term. That matches any element carrying an href attribute — a <link> in the head, a <span href>, or a custom element — not just focusable links. Only <a href> and <area href> are actually focusable via href.

useFocusTrap feeds this selector straight into querySelectorAll to compute trap boundaries (the first/last tab stop). A non-focusable element carrying href could therefore be picked as the first or last "tab stop", breaking Tab-wrap inside a trap — the boundary element never receives focus, so the wrap condition never fires.

This narrows the term to a[href], area[href]. The rest of the selector is unchanged.

Changes

• packages/core/src/hooks/focusableSelector.ts: [href] → a[href], area[href] in FOCUSABLE_SELECTOR. The doc-comment describes this term as "link", which stays accurate.
• packages/core/src/hooks/useFocusTrap.test.tsx: added a FOCUSABLE_SELECTOR href matching block — asserts the selector matches <a href>/<area href> but excludes <span href> and <link href>, plus an end-to-end check that focusFirst lands on an <a href> inside a trap.

Test plan

• node_modules/.bin/vitest run --root . packages/core/src/hooks — 118 pass (12 files), including the 2 new tests. useFocusTrap.test.tsx now has 8 tests (was 6). This is the only importer of focusableSelector, and its tests live in this directory.
• Confirmed failing-first: temporarily reverting the selector to [href] and running the new test fails on expect(matches).not.toContain(span), proving it catches the regression.
• tsc --project packages/core/tsconfig.json --noEmit — clean.
• eslint on both changed files — clean.

Notes

Found during a broader a11y audit of core hooks. Scoped to this one selector fix — related findings (e.g. excluding aria-disabled elements) are intentionally left out.

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