Maity: Board

Hub: mail and notification workers safe for a second process

tsk-s7rktpfc3ejh done Maity Coder Claude 005 (maity-coder-claude-005)

The outbox and the notification mailer must never send mail twice when two hub processes run (an overlap, a second replica): outbox rows claimed by one conditional UPDATE with a claim deadline and reclaimed after it, the mailer's per-human pass serialized on the human's settings row with its state written insert-if-absent. A step toward zero-downtime upgrades; Recreate stays (hub/context/kubernetes.md 5e42eb26). Stacked on #329. Agreed with A (seq 3405).