pr check from a job branch that is not the PR

The Broader Goal at the End of the Previous PR

#1449 let review sandboxes run synlynk pr check without writing shared todo.md. The remaining hole was that the same command still failed closed on every dispatched reviewer: the job worktree is on dispatch/<harness>/job-<id>, not the PR branch, so gh pr view and gh pr checks <branch> cannot see CI.

Strategic Shifts in This PR

None. #1432 already named the fix: do not depend on branch identity.

What This PR Shipped

_current_pr_number still tries gh pr view, then looks up HEAD via GET /repos/.../commits/{sha}/pulls. synlynk pr check --pr N skips lookup. _extract_verified_by_ci / the QA gate use gh pr checks <number> when a PR number is known, so a dispatch/codex/job-* checkout of the same SHA sees the same CI as the PR branch.

Brainstorm Visuals Used

None.

What This Achieved on the Path to Autonomy

Dispatched QA can run synlynk pr check from the job worktree and get a real CI verdict instead of "undeterminable — failing closed."

Strategic Note: The Goal at the End of This PR

#1432 closed. Identity (#1436) is the remaining review-dispatch item: QA actions:read cannot rerun flaky CI, and merge jobs still classify as review_posted on the board.