- Remove is_dm column from channels table (dm detection by member count)
- Rename member name column to userinfo — extensible json_flat format
- Add json_flat.c/h library for compact JSON serialization
- Fix join_sig message format: use ch_x25519+ch_ed25519 instead of channel_id string
- Remove name from join_msg body (now in userinfo via json_flat)
- Update chat_core, chat_sync, member_sync, db_manager to new format
- Add topo_strategy.txt — архитектурные заметки по топологии
Replace etcp_router_bind/etcp_route_send/etcp_router_unbind with
direct etcp_bind/etcp_send/etcp_unbind + find-conn-by-node_id helpers.
Same approach as db_sync (0x20). Service IDs unchanged (0x30, 0x31).
Evgeny