fix: preserve acknowledged terminal PR snapshots

[steingran]

Summary

• preserve done for an open PR only when its persisted review-ready repository, PR number, and head SHA still match
• reopen a changed or unknown terminal snapshot into accountable active work using the durable follow-through owner when available
• keep repeated matching terminal and changed-head continuation polls idempotent across issue-linked and direct-PR sync

Root cause

The status resolvers mapped every review-ready open PR to in_review, even after an independently acknowledged Paperclip completion. The existing action fingerprint contains a hash of the head but cannot safely serve as a comparison baseline.

Verification

• pnpm typecheck
• pnpm test
• pnpm build

The regression fixture uses AIG-761's acknowledged PR #77 head 65cca42353b54bea1370a7a78442eb7499aa6565, verifies no transition comment or wake on a matching green snapshot, then verifies a changed green head produces one owner-assigned active continuation with no churn on the next identical poll.