feat(pr-review): track open question status and label the sticky comment

[Troublor]

Summary

Two follow-ups to the PR review action, both about telling a reader what state something is in.

Open questions now have a lifecycle. Previously an Open question was rendered once into a review body and forgotten. The author would answer it in a reply, but the original question sat there unchanged with no indication it had been resolved.

• Each question gets a stable ID and a hidden marker on its status line, plus a manifest entry recording which review asked it — the same durable treatment findings already had.
• The model must return a prior_questions disposition (open / answered / withdrawn, with a one-line reason) for every open question, mirroring the existing prior_findings contract. An omitted question stays open.
• The deterministic publisher then rewrites that one line in the original review body: ❓ **Open question · Medium confidence** becomes ✅ **Answered** — <reason>. Editing a submitted review body creates no new review and no new notification. The rewrite reproduces the same marker line, so it is idempotent; a GitHub failure leaves the entry pending and the next round retries it, and a question whose asking review cannot be found settles as unavailable rather than retrying forever.
• A question that is already open is no longer re-asked. Re-asking orphaned the copy the author was actually answering.

The sticky comment says it is a living comment. It is rewritten in place on every run, but nothing said so, which reads as confusing or stale to anyone meeting it mid-thread.

• It now opens with an explicit note that the workflow keeps this single comment up to date instead of posting a new one each round, and that no reply is needed there.
• It carries an update timestamp alongside the reviewed range, splits this round's counts into findings and questions, and rolls up the questions still awaiting an answer with a link to the review that asked each one.
• The status body is rendered at publish time rather than compile time, so those links can reference the review ID assigned in the same run.

Test plan

• python3 -m unittest discover -s .github/actions/claude-pr-review -p 'test_*.py' — 66 tests pass, 14 of them new: marker stability, no-duplicate-question, disposition handling, unknown/omitted dispositions, in-place rewrite, idempotent re-application, missing marker, failure retention, stale-head propagation, sticky banner and roll-up, and skip-mode behaviour.
• mise run lint — links, markdownlint, and prettier clean.
• This repo dogfoods the action through the local ./.github/actions/claude-pr-review path, so this PR exercises the new publish path against itself.

Note that consumers pin @main, so this goes live for every consumer repo on merge.

[github-actions]

Claude review status

✅ Review clean

Last reviewed: head 3cc74510

New this round: 0 · Resolved this round: 0 · Open questions: 0