Turn on automatic UK promotion under d1344 (replay policy, known gaps, review bounds, liveness) #634

Follow-up to #574 (UK candidate qualification), under cos d1344. That decision delegates the CI plan's methodology calls to the workstream sessions, each with independent review agreement and receipt-recorded exceptions. It also decided that automatic promotion is turned on once #574 lands on its gates.

Work:

• Replay gate policy d1344-replay-regressions-v1 (agreed 15 October after two independent reviews). Fail on the regressions a scorecard receipt identifies: mapping flags, lost results, lost responses and incomplete grids. Call a gap known only on base-side evidence. Send every other flagged move to a named reviewer. Record the policy id and the SHA-256 of its text in each receipt.
• Known gaps: vendor policyengine-scorecard's diff.base_events and the candidate's missing/unsupported measure-year lists (scorecard#183) once they merge, and implement the exact known-gap test.
• Review bounds: adopt the metrics review bounds and W3's suppression rules when W3's approved aggregate-impact commit lands.
• Automatic promotion: set promotion.automatic: true, with the d1344 basis recorded.
• Liveness: requalify candidates whose baseline went stale, so automatic promotion doesn't stall.