[Improve] Notify users when PR auto-resolve continues

[roomote-roomote]

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

What changed

When auto-resolve starts work on later PR review feedback, the task now posts the existing "New review feedback - I'm on it" update to its originating communications thread after dispatch succeeds. Canonical delivery checkpoints the provider message before completion, while initial feedback and web-only tasks retain their existing behavior.

Why this change was made

Fast-parent delivery returned before the established communications posting path ran, so users could not see when automatic work continued onto subsequent review feedback. Missing Slack message IDs now trigger retries, and the durable provider-message checkpoint no longer depends on the posting worker retaining its lease.

Impact

Users with a connected task communications channel receive one contextual continuation update identifying the PR feedback being handled. Slack null results remain retryable, while Telegram completion retries skip a continuation message that was already checkpointed.

Validation

• BullMQ PR review notification suite (49 tests), Slack footer suite (3 tests), and canonical database delivery suite (18 tests)
• BullMQ, SDK, database, and Slack package typechecks
• pnpm lint
• Pre-push oxlint, residual lint, fast typechecks, and knip

[roomote-community]

No new code issues found. See task

• A Slack continuation post that returns no message ID is still marked complete instead of being retried (apps/bullmq/src/jobs/pr-review-notification.ts:917).
• A continuation post can still be duplicated on Telegram when its checkpoint fence is lost, because Telegram ignores the supplied idempotency key (apps/bullmq/src/jobs/pr-review-notification.ts:915).

_{Reviewed 1132329}

[roomote-roomote]

Fixed both provider-specific findings in 1132329: Slack continuation posts that return no message ID now fail and requeue, while the provider-message checkpoint no longer requires the original lease, allowing Telegram completion retries to skip the already-sent post. Added focused Slack null-result, Telegram completion-retry, and lease-independent database checkpoint coverage.