Companion to the dispatcher-side outbox change: adds the
delivery_attempts table migration, Store.BeginDeliveryAttempt/
CompleteDeliveryAttempt/ReconcileStaleDeliveryAttempts, and wires
ReconcileStaleDeliveryAttempts + Config.Outbox into mavend startup
before the tick loop resumes.
Vikunja #270.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ghELqYhZNLub2TXGMazqA
kami