add etcp_router service routing layer + remote TCP proxy (uip+socket via router)

etcp_router: routable service packets with dst/src node_id
- etcp_router_bind/unbind: per-instance service handler registry
- etcp_route_send: send to node by id via BGP routing
- multi-hop forwarding through intermediate nodes
- loopback optimization (dst==self dispatches directly)

remote_proxy: exit node creating OS sockets on demand
- handles CONNECT/DATA/CLOSE via etcp_router
- non-blocking socket connect with uasync callbacks
- echo back response data to requesting node

tcp_proxy: etcp_transport for remote proxy
- via_node_id in mapping selects between sock/etcp transport
- unified handler for both tcp_proxy and remote_proxy roles
- config: forward = port -> ip:port via NODE_HEX [remote_proxy] section

tests: test_etcp_router (20 pkts bidirectional), test_remote_proxy (echo)

src/config_parser.h

@@ -82,6 +82,14 @@ struct CFG_ALLOWED_KEY {
     struct CFG_ALLOWED_KEY *next;
 };
 
+#define MAX_TCP_PROXY_MAPPINGS 32
+struct tcp_proxy_mapping_config {
+    uint16_t local_port;
+    char     remote_ip[64];
+    uint16_t remote_port;
+    uint64_t via_node_id;  // 0=локальный прокси, !=0=удаленный прокси через эту ноду
+};
+
 struct global_config {
     char name[16];                    // Instance name
     char my_private_key_hex[MAX_KEY_LEN];
@@ -143,6 +151,18 @@ struct global_config {
         uint16_t external_port;
     } nat_forwards[MAX_NAT_FORWARDS];
     int nat_forward_count;
+
+    // TCP proxy configuration ([tcp_proxy] section)
+    int      tcp_proxy_enabled;
+    char     tcp_proxy_tun_name[16];
+    char     tcp_proxy_tun_ip[64];
+    int      tcp_proxy_mtu;
+    int      tcp_proxy_eim_timeout;
+    struct   tcp_proxy_mapping_config tcp_proxy_mappings[MAX_TCP_PROXY_MAPPINGS];
+    int      tcp_proxy_mapping_count;
+
+    // Remote proxy (exit node) configuration ([remote_proxy] section)
+    int      remote_proxy_enabled;
 };
 
 struct utun_config {