Tasks: a parked work item is owned by the instance that accepted it

Each task names the requirement it satisfies and the testing-plan row that proves it.

Task list

[x] A1: guard. _accepted_here and its clause in _authority. Req: R1, R3 · Test: T1, T3 · Depends: —
[x] A2: cancellation. _cancel_pending_start in close_ticket; startCancelled in the result. Req: R2 · Test: T2 · Depends: A1
[x] A3: integration. test_parked_closure_integration.py over the real dispatcher. Req: R2.5, R2.6, R3.2 · Test: T4 · Depends: A2
[x] A4: docs. ticket.md, capabilities/cli.md, decision-141, the MCP tool's docstring. Req: NFR · Test: T7 · Depends: A2
[x] A5: verify. T5–T7, evidence. Depends: A1–A4