pr-queue-hygiene: stale conflict marker never cleared on deconflict; comment lookup unpaginated #432

Follow-up to #427 / #429, from the code review of #240. Two pre-existing defects remain in scripts/pr-queue-hygiene.mjs:

1. Stale marker never cleared on deconflict (main(), ~line 195): when a PR stops conflicting, the loop continues without removing the first-conflict marker comment or the needs-rebase-or-close label. If the PR later reconflicts, hoursSince() is computed from the old marker's timestamp, so the PR is flagged as >48h stale immediately instead of getting a fresh 48-hour window.

2. Comment lookup reads a single unpaginated page (main(), ~line 181): issues/{n}/comments?per_page=100 with no page loop. Issue comments sort ascending, so on a PR with more than 100 comments the marker at the end is never seen — every run posts a duplicate marker and the 48h gate never fires.

Blast radius is labels/comments only (the script never closes PRs), but both defects defeat the 48h grace-period semantics.

Suggested fix: on the non-conflicting path, delete or neutralize the marker (or append a resolved marker and use the latest observation), and paginate the comment listing.