Fix: Client config uses fixed port 9002, add protective comments

- Changed client server port from 0 (unsupported) to 9002 (fixed)
- Added comments explaining importance of fixed ports vs random ports
- ETCP now uses proper port configuration for client-server setup

tests/test_etcp_two_instances_fixed.c

@@ -70,8 +70,10 @@ int main() {
     fclose(f);
     
     // Create client config
+    // ВАЖНО: Использовать фиксированный порт, случайные порты (0) не поддерживаются
+    // Клиентский сервер должен использовать другой порт, чем удаленный сервер
     f = fopen("/tmp/c.conf", "w");
-    fprintf(f, "[global]\nmy_node_id=0x2222222222222222\nmy_private_key=1313912e5d34768983b0e06530a48c77816d228a5b5605e1ab3dc443d107a3dc\nmy_public_key=dde6cec8a9023339a758f60883ef41534d24a1ffdc09bbb787a5c24ddfd891e3092461835a97d37944c681fc6b2c1f5acde8ad192f7d2cdc9920aa0d3ff78e99\ntun_ip=10.99.0.2/24\ntun_ifname=tun98\n\n[server:local]\naddr=0.0.0.0:0\ntype=nat\n\n[client:test]\npeer_node_id=0x1111111111111111\nkeepalive=1\nlink=local:127.0.0.1:9001\n");
+    fprintf(f, "[global]\nmy_node_id=0x2222222222222222\nmy_private_key=1313912e5d34768983b0e06530a48c77816d228a5b5605e1ab3dc443d107a3dc\nmy_public_key=dde6cec8a9023339a758f60883ef41534d24a1ffdc09bbb787a5c24ddfd891e3092461835a97d37944c681fc6b2c1f5acde8ad192f7d2cdc9920aa0d3ff78e99\ntun_ip=10.99.0.2/24\ntun_ifname=tun98\n\n[server:local]\naddr=127.0.0.1:9002\ntype=nat\n\n[client:test]\npeer_node_id=0x1111111111111111\nkeepalive=1\nlink=local:127.0.0.1:9001\n");
     fclose(f);
     
     struct UASYNC* sua = uasync_create();
@@ -88,6 +90,9 @@ int main() {
     init_connections(client_instance);
     
     printf("✓ Both instances initialized\n");
+    printf("✓ Server listening on 127.0.0.1:9001\n");
+    printf("✓ Client local server on 127.0.0.1:9002\n");
+    printf("✓ Client connecting to server at 127.0.0.1:9001\n");
     
     uasync_set_timeout(sua, 1000, NULL, monitor_connections);