heather: jitsi-jvb add network alias 'jvb' (nginx colibri-ws proxy needs it)

nginx template in jitsi-web hardcodes proxy_pass http://jvb:9090 for
/colibri-ws/jvb/* but service is named jitsi-jvb → DNS NXDOMAIN → 502.
Official compose names service 'jvb'; arion service key is jitsi-jvb so
add network alias 'jvb' to fix bridge channel.

hosts/heather/arion-compose.nix

@@ -229,7 +229,7 @@
       ];
       service.volumes = [ "jitsi-jvb-config:/config" ];
       service.depends_on = [ "jitsi-prosody" ];
-      service.networks = [ "meet-jitsi" ];
+      service.networks.meet-jitsi.aliases = [ "jvb" ];
       service.env_file = [ "/var/lib/jitsi-secrets/jitsi.env" ];
       service.environment = {
         TZ = "Europe/Moscow";