Three fixes for group DM data integrity and display:
1. processOwnershipTransferEvent: use resolveOrCreateReplicatedUser instead
of resolveLocalUser to guarantee a valid ownerId. The previous ?? null
fallback converted group DMs into 1-on-1s when resolution failed.
2. Self-healing migration: detect group DMs with UUID-format federated_id
but NULL owner_id (corrupted by the old fallback) and restore owner from
the first remaining member. Found and repaired 7 across both instances.
3. Sidebar: group DMs with 0 other members (last person standing) now show
as "Empty Group" instead of being hidden. 1-on-1 DMs with 0 others are
still correctly filtered out.
Jannis Braun
41658ec2ef