Remove the owner-only gate on POST /api/dm/:id/members. The S2S relay
already accepts member_add from any HMAC-verified peer, and the UI
already shows the add button to all group DM members. Only the
server-side check was blocking non-owners.
Add federation.md section 8b covering dm_close/dm_reopen relay events:
payload, outbound queueing via queueDmCloseRelay, inbound processDmCloseEvent/
processDmReopenEvent handlers (lookup-only identity resolution, silent
no-ops on missing channel/user/membership), and the processCreateEvent
closed-state reopen bug fix.
Update dm-system.md soft-close section with federation behaviour: relay
to peers for both close and reopen, relayed-message reopen in
processCreateEvent, and the federatedId-only guard for legacy DMs.
Jannis Braun