mirror-history: end-to-end validation (mirror -> promote -> delete -> re-run)

[toddysm]

Part of #157.

Validate the whole flow end-to-end.

Scenario

1. Mirror an image into quarantine/<image> (history entry recorded).
2. Promote it and delete the tag from quarantine (:mirror-history keeps the package alive; no last-tagged-version delete workaround needed).
3. Re-run the mirror: it reports skipped (already synchronized) instead of re-copying.
4. force re-run still copies and records.
5. Dashboard Acquisition view shows the per-repo synchronized history and no longer shows a history-only package as awaiting promotion.

Also: get_errors clean, actionlint + shellcheck -S warning clean on new/changed run blocks, per-service pytest green.

Depends on: #159, #161.