Add NATS-over-WebSocket compose for Coolify

Configures a single NATS 2.10 service exposing a WebSocket listener on
:8080 (no_tls; Traefik terminates TLS at nats.volcanic.tes.gd) with
env-driven username/password auth and a persisted JetStream store.

nats-server.conf

@@ -0,0 +1,21 @@
+server_name: "nats-volcanic"
+
+port: 4222
+http_port: 8222
+
+jetstream {
+  store_dir: "/data"
+  max_memory_store: 256MB
+  max_file_store: 4GB
+}
+
+websocket {
+  port: 8080
+  no_tls: true
+}
+
+authorization {
+  users = [
+    { user: $NATS_USER, password: $NATS_PASSWORD }
+  ]
+}