Finalize remote Huddles only on explicit leave; treat archived as terminal - #9384

Stacked on #9376 remote Huddle cleanup. It fixes two blocking findings from review of 04321aa.

Summary

Only an explicit leave ends a remote Huddle. On 04321aa, when a control stream ended with peers still registered, the owner archived the channel and published the ended event (48103). That happens when the ingress relay restarts (Huddle audio sockets aren't drained, so they never send UnregisterPeer), crashes, or loses its relay-to-relay link. The ingress tells its clients to rejoin, but the rejoin then finds the channel archived. Now only an UnregisterPeer frame finalizes the room. Loop-exit teardown goes back to main's behavior: it removes the room and releases the lease, without ending the Huddle. On the ingress, a SessionEnded teardown (the local client's control sink closed while a roster update was queued) now sends the clean close first, so a real leave that loses the reader's select race still unregisters.

An already-archived channel is a terminal outcome. The mobile end flow archives the channel itself, often before the last remote connection closes. archive_channel_if returned "channel is already archived" as an error, so the finalizer kept the empty room and its renewing lease with no retry. It now returns Ok(false) when the locked row is already archived. The finalizer then releases local resources and publishes no second ended event. This also fixes main's equivalent leak on the local path.

Out of scope, per review: retrying after a failed archive, the Redis validation inside the archive transaction, and the draining-owner behavior change.

Related issue

N/A. Review findings on #9376 remote Huddle cleanup.

Testing

• remote_last_leave_ends_huddle_and_releases_owner_resources (new Postgres journey, runs in the postgres-ci lane with Redis): the owner's local participant leaves, then the last remote participant leaves cleanly through the production HuddleControlAcceptor and finalizer. The unarchived row ends the Huddle once. The creator-archived row publishes no relay ending. Both rows release the room and lease.
• remote_only_stream_close_releases_owner_room_and_lease now covers both a bare stream drop (room and lease released, no ending) and a clean leave (exactly one ending).
• conditional_archive_rechecks_authority_before_committing asserts that archiving an already-archived channel returns Ok(false).
• Ran each guard both ways: removing the already-archived early return fails the creator-archived row and the DB test, and letting stream loss finalize fails the bare-drop row.
• Full non-ignored buzz-relay and buzz-db suites pass, and clippy is clean. Not validated on a live multi-relay call.

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