When a ticket is handed to a live Claude pane (T-327), advance it to
in_progress on the receiving side of the bus — gated on acceptance, so a
pick-up with no live session stays a quiet no-op and never mutates state.
Only a not-yet-started ticket (backlog/ready) transitions, so re-picking
up a review/done ticket doesn't drag it backwards. On success it publishes
(builtin.tickets, changed) so the sidebar refreshes.
The handler logic moves into a testable applyTicketPickUp() seam; the
sidebar button now carries the current status in the pick-up payload.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>