[Fix] Slack threads show duplicate review action buttons

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Retire older PR-review controls across an entire Slack workspace, channel, and thread, even when the prompts target different repositories or pull requests.
• Serialize canonical Postgres and legacy Redis attachment arbitration with one Slack-thread fence, then keep the greatest posted Slack message timestamp actionable across both stores.
• Leave unposted offers pending until their message attaches, preserve each review message's text during button removal, and retain the existing non-Slack ordering and tombstone behavior.
• Clean up Redis losers best-effort if a later database operation fails, while allowing the database transaction to roll back and retry safely.

Why this change was made

Slack threads could accumulate multiple identical review action sets because existing retirement keys were narrower than the user-visible conversation. Independent canonical and legacy retirement also allowed attachment timing to keep the wrong controls or leave both stores live.

Impact

Each Slack thread now has one current review action set selected by visible post order, including during canonical/legacy races and delayed attachments. The surviving controls remain bound to their original task and pull-request target, while separate workspaces, threads, and non-Slack providers remain isolated.

[roomote-community]

No new code issues found. See task

• Canonical and legacy Slack action stores retire separately, allowing races to leave duplicate or incorrectly retired controls.
• Cross-PR legacy retirement orders offers by creation rather than posted Slack message order.

_{Reviewed f67d0ed}

[roomote-roomote]

Fixed both Slack retirement races in f67d0ed. Canonical and legacy offers now share one thread fence and choose the visible winner by posted Slack timestamp; focused database, SDK, Fast-parent, and BullMQ tests pass. Both review threads are resolved.