feat(builtin): NAT node returns its interface IP info in asdict()

NAT now includes an 'interfaces' field in its response, filtered to
contain only the mapped NAT interface (virbr0 on Linux, vmnet8 on
macOS/Windows). This lets connected nodes discover the NAT subnet
and gateway address without needing to list all host interfaces.

The field format mirrors Cloud.asdict(): name, type, special, and
ip_addresses list (both IPv4 and IPv6).

gns3server/compute/builtin/nodes/nat.py

@@ -87,6 +87,23 @@ class Nat(Cloud):
         return True
 
     def asdict(self):
+
+        nat_interface = self._ports_mapping[0].get("interface", "") if self._ports_mapping else ""
+
+        host_interfaces = []
+        network_interfaces = gns3server.utils.interfaces.interfaces()
+        for interface in network_interfaces:
+            if interface["name"] == nat_interface:
+                host_interfaces.append(
+                    {
+                        "name": interface["name"],
+                        "type": interface["type"],
+                        "special": interface["special"],
+                        "ip_addresses": interface.get("ip_addresses", []),
+                    }
+                )
+                break
+
         return {
             "name": self.name,
             "usage": self.usage,
@@ -94,4 +111,5 @@ class Nat(Cloud):
             "project_id": self.project.id,
             "status": "started",
             "ports_mapping": self.ports_mapping,
+            "interfaces": host_interfaces,
         }