fix(j5): reconcile archive racing an existing thread’s first Squadron assignment #179

A thread archived before it has a Squadron home can acquire an active A2A membership if onboarding assignment or join_squadron races archive. Both paths check the thread before registering, but archive can commit between that check and the join transaction.

The lifecycle reactor currently skips thread.archived for an unregistered thread and advances its replay cursor. If registration commits afterwards, the orchestrator thread is archived while the directory lists active membership. Delivery transport refuses the archived target; this is misleading addressability rather than successful delivery. A later unarchive/delete reconciles the home.

Fix the shared lifecycle/registration boundary for both entry points. Preserve immutable homes, reversible archive, and legacy permanent retirement. Avoid adding a separate lifecycle implementation to the onboarding route. Add a deterministic regression forcing archive consumption before registration, plus the opposite ordering and unarchive/replay coverage. A retained pre-registration lifecycle fact is one possible approach; investigate the smallest shared solution.

Identified in the independent Fable review of the onboarding follow-up on draft PR #178; the existing join_squadron has the same window. Relevant code: LifecycleService.handleStoredEventInternal / replayCommittedEventsRaw, SquadronJoinService.joinExistingThread, and the importer assignment route.