chore(queue): split nonessential hardening from edit fencing

[Fclem]

Branch surgery completed.

• Focused PR branch feature/imp-prevent-sends-du-zcf now points to 5f5b4ca4a and excludes the unrelated office/agent-runtime merge artifacts.
• Reviewer follow-ups from issuecomment-5595864240 remain on the focused branch: immutable task/session identities in queue E2E helpers, lifecycle queue-reservation settlement during recovery, workflow transfer fencing by session identity, and desktop/mobile post-save Auto-run expectations.
• Required PostgreSQL queue cleanup hardening was retained in the focused branch because removing it broke durable claim purge, active-transfer fencing, and pending-move cleanup tests.
• The separate dependent branch queue-hardening-pr points to dad8fe319; relative to the focused branch it contains only the nonessential CI auto-fix row cleanup and queue schema-probe dialect change.
• The follow-up branch is pushed to the contributor fork. An upstream stacked PR cannot be opened until feat(queue): fence queued message editing against concurrent sends kdlbs/kandev#3480 merges because GitHub upstream PRs cannot target a branch that exists only in the fork. Creation link: https://github.com/Fclem/kandev/pull/new/queue-hardening-pr