- chat_conn_mgr.c/h: new connection manager (1 per instance, global in g_cc)
- cm_rotation() — single rotation method: random addr pick, INIT, retry
- 10 parallel slots per node (CM_MAX_PARALLEL), evict worst RTT on excess
- DEAD slot reuse before close — close only when replacement ready
- per-connection DOWN callback via etcp_conn_add_down_cbk
- background ping cycle: random node→random addr RTT measurement
- chat_core.c: added g_cc.conn_mgr field, init/destroy/getter
- chat_sync.c: migrate to new API, add_node() at WELCOME/JOIN/PEER_UPSERT
- Removed old ca_state/ca_ctx/ca_* single-flight code
Evgeny