feat: PING/PONG RTT exchange + burst sender + TCP server; fix INIT peer_id offset

- etcp_connections: add flags byte to PING/PONG wire format (WANT_RTT/SEND_RTT)
- etcp_connections: add etcp_link_burst_start/check for BDP measurement
- etcp_connections: add tcp_server_on_link for STCP→ETCP bridge
- topo_node: add ping_request_cbk/ping_update_rtt for live RTT tracking
- topo_node: add last_ping_time field in connectivity
- topo_node_sqlite: extend DB schema for RTT data
- fix: INIT path read peer_id from offset 1 (not 2), PING offset stays 2

src/routing_layer/topo_node.h

@@ -31,6 +31,7 @@ extern "C" {
 #include "secure_channel.h"
 
 struct TOPO_GROUP;
+struct TOPO_GROUPS;
 struct ETCP_SOCKET;
 struct UTUN_INSTANCE;
 
@@ -100,9 +101,12 @@ struct TOPO_CONNECTIVITY {
     uint64_t nat_probe_time;
     uint64_t real_probe_time;
     uint64_t ping_req_time;
+    uint64_t last_ping_time;   // время последнего успешного пинга (0.1ms timebase)
     void*    probe_list;
 };
 
+#define PING_TTL_TB (86400ULL * 10000ULL)  // 1 день в 0.1ms units
+
 // =======================================================================
 // Протокольные структуры (wire-format, packed, без next)
 // =======================================================================
@@ -270,6 +274,9 @@ int topo_group_update_my_nodeinfo(struct UTUN_INSTANCE* instance, struct TOPO_GR
 void topo_node_dump_all(struct TOPO_GROUP* group);
 int  topo_node_format_all(struct TOPO_GROUP* group, char* buf, size_t buf_size);
 
+int  topo_node_ping_request_cbk(struct TOPO_GROUPS* groups, uint64_t node_id);
+void topo_node_ping_update_rtt(struct TOPO_GROUPS* groups, uint64_t node_id, uint16_t rtt);
+
 #ifdef __cplusplus
 }
 #endif