feat(desktop): redesign the clarify prompt + fix its awaiting-input states

[OutThisLife]

Summary

The desktop clarify prompt (the inline "answer this question" panel) was visually
out of step with the rest of the chat and had a few awkward lifecycle states.
This reworks both: a clean rebuild on the shared design tokens, plus modeling a
pending prompt as paused-on-you rather than an in-flight turn.

What changed

Redesign (clarify-tool.tsx)

• Rebuilt on the shared --ui-* / --conversation-* tokens — compact panel, no
  bespoke card/animated ring, reads as part of the transcript.
• Letter-key badges (A/B/C…) that double as a/b/c… keyboard
  shortcuts; selection lives on the badge alone (solid primary; outlined while
  "Other" is focused-but-empty).
• "Other" is an inline content-sizing field (CSS field-sizing, same
  primitive as the commit bar / search field) — no view swap, no layout shift on
  focus.
• Picking an option selects instead of auto-sending; a Continue button (or
  Enter) confirms. Focusing "Other" deselects any choice, so the two inputs can
  never both look selected.
• The panel settles into the standard tool block once the turn stops running, so
  a stopped turn never strands a live, unanswerable prompt.

Awaiting-input behavior

• New $activeSessionAwaitingInput (mirrors the pet's awaitingInput concept,
  scoped to the active session) composed from the existing clarify/approval/
  sudo/secret atoms.
• The "thinking" stall timer is suppressed while a prompt waits — the agent
  isn't working, it's waiting on you.
• Esc no longer interrupts the run while a prompt is pending, so you can leave
  a question parked (per-session) and come back to it. Stop and turn end clear
  the session's prompts + needsInput, so a resolved/aborted turn can't leave a
  dead panel or a stuck "needs input" dot.

Notes / out of scope

• Clarify remains single-select — the clarify tool's protocol returns one
  string (max 4 choices + Other) across all surfaces (CLI/TUI/gateway/desktop).
  Real multiselect is a separate cross-surface change; the new UI is already
  shaped to drop in checkboxes when that lands.

Test plan

• tsc typecheck clean
• eslint clean on all touched files
• vitest — clarify/prompts/approval/prompt-actions/state-cache/thread-loading (86) + new $activeSessionAwaitingInput contract tests
• Manual: pick via mouse + a/b/c; type in Other (grows, no shift); Continue/Enter; Skip; hit Stop mid-clarify (panel settles, dot clears); switch chats and return (prompt still parked)

Screenshots

To attach: the rebuilt panel (choices + letter badges), the content-sizing "Other" field, and a selected/Continue state.