feat(desktop): keyboard navigation for clarify choices

[OutThisLife]

Salvages #64346 by @mapu-og (Mapurite; cherry-picked, authorship preserved).
Re-authored onto the merged ChoiceButton (#69769) and the sanitized choice
pipeline (#69497) — the original edited the pre-refactor inline <button>.

What it adds

A keyboard cursor over the clarify options on the live card:

• ↑/↓ move a visual highlight across the choices and the trailing "Other"
  free-text row (wraps around).
• 1-9 and A/B/C… pick a choice directly; the trailing number/letter
  jumps into the "Other" field.
• Enter confirms the staged answer, or acts on the highlighted row (a choice
  responds immediately; "Other" focuses the textarea).
• Full a11y: aria-current, aria-keyshortcuts (e.g. A 1), and
  data-highlighted on the active row.

The global key handler stands down whenever a focusable control (any field,
choice button, or the action bar) already has focus, so it never eats keystrokes
meant for the composer, the Other box, or a tabbed-to button.

Tests

clarify-tool.test.tsx — arrow cycling + aria wiring, number-select + Enter
confirm (asserts the clarify.respond payload), Other focus leaves typing keys
alone, and the handler yields while an action button is focused.

This is a feature (not a bugfix); it layers cleanly on top of the clarify
fixes. Stacked on #69796 → #69795; review/merge those first.

Supersedes #64346.

[github-actions]

૮ >ﻌ< ა ci review

_{ran on c63cd3c}

ℹ️ Info

Desktop E2E visual evidence · View test artifacts · View job

1 visual diff.

_{inline evidence is publishing...}

[alt-glitch]

This was generated by AI during triage.

Related to open #65778: both add Desktop clarify keyboard navigation, but this patch uses active-surface arbitration while #65778 also changes settled-choice/history behavior. Please choose the intended UI semantics; they are not duplicate patches.