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

web/projects/ui/src/app/services/api/api.fixures.ts

@@ -2137,7 +2137,7 @@ export namespace Mock {
                   host: 'adjective-noun.local',
                   port: 1234,
                   metadata: {
-                    kind: 'private-domain',
+                    kind: 'mdns',
                     gateways: ['eth0', 'wlan0'],
                   },
                 },