Adds a new resolution step before the legacy 2-member-identity fallback:
if the event's dmChannelId is an alternate-origin local id for a DM
whose primary is in dmChannels, route the message to the primary via
resolveDmChannelId. Covers 1-on-1 AND group DMs uniformly — closes a
pre-existing phantom-sidebar-entry bug for group DMs in multi-instance
sessions and handles post-failover routing when the reconnected original
origin's WS still addresses the DM by its old local id.
Jannis Braun
b1844e126f