feat: add mdns hostname metadata variant and fix vhost routing

- Add HostnameMetadata::Mdns variant to distinguish mDNS from private domains
- Mark mDNS addresses as private (public: false) since mDNS is local-only
- Fall back to null SNI entry when hostname not found in vhost mapping
- Simplify public detection in ProxyTarget filter
- Pass hostname to update_addresses for mDNS domain name generation

core/src/net/gateway.rs

@@ -1005,9 +1005,10 @@ impl NetworkInterfaceController {
                 .as_network_mut()
                 .as_gateways_mut()
                 .ser(info)?;
+            let hostname = crate::hostname::Hostname(db.as_public().as_server_info().as_hostname().de()?);
             let ports = db.as_private().as_available_ports().de()?;
             for host in all_hosts(db) {
-                host?.update_addresses(info, &ports)?;
+                host?.update_addresses(&hostname, info, &ports)?;
             }
             Ok(())
         })