heather: jitsi — networks is top-level option (not docker-compose.networks)

Arion: `networks` — top-level опция как `services`, не внутри docker-compose.
service.networks принимает listOf str или attrsOf с aliases. meet.jitsi → meet-jitsi
(имя без точки, docker-compose требование к network names).

hosts/heather/arion-compose.nix

@@ -258,7 +258,7 @@
       ];
       service.volumes = [ "jitsi-jvb:/config" ];
       service.depends_on = [ "jitsi-prosody" ];
-      service.networks = [ "meet.jitsi" ];
+      service.networks = [ "meet-jitsi" ];
       service.env_file = [ "/var/lib/jitsi-secrets/jitsi.env" ];
       service.environment = {
         TZ = "Europe/Moscow";