V3 docs: record the settled queue subsystem in docs/QUEUE.md

[Loufe]

Goal

The queue subsystem shipped through #41, #63, #66, and #67, all closed, so its settled behavior has no document: the job coordinator, claim and run sequence, enqueue filtering, per-item editing, reorder rules, and stop paths exist only in code and ADRs. Record them as one contract doc so Analysis, UI, and History work can cite it instead of rereading the coordinator.

Work

• Describe the job coordinator: claim, phase sequence, terminal settlement, and where each boundary sits across crfty-core and crfty-engine.
• Describe enqueue filtering and the typed add summary, citing ADR-013, filter queue adds at enqueue.
• Describe the queue shape invariant, per-item editing, drag reorder, and active-item immutability.
• Describe the shipped stop and force-stop paths and their containment boundary, noting ADR-018, unify job cancellation and completion, as the pending direction under V3 engine: four cancellation mechanisms and twin job handles want one shared supervision kit #85.
• Verify every statement against crates/ before writing it; anything unverified goes to docs/design/ instead.

Acceptance

• docs/QUEUE.md covers the coordinator, enqueue filtering, item editing and reorder, and stop behavior.
• Every claim is verified against shipped code or an accepted ADR.
• ADRs are cited by number and short title, never restated.
• docs/ARCHITECTURE.md links docs/QUEUE.md from its queue section.