Three fixes for 3-relay chain (R1→R2→R3):
1. Room lookup in handle_datagram: hub relay (R2) has no local
participants, so active_rooms() was empty and datagrams were
silently dropped. Now also checks global_rooms config directly,
allowing hub relays to forward without local clients.
2. Multi-hop forwarding: removed active_rooms filter — forward to
ALL connected peers except source. The receiving peer decides
whether to deliver or forward further.
3. Android relay_label: native RoomMember now includes relay_label
from RoomUpdate signal. Kotlin UI reads it for relay grouping.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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