Add a three-node NATS JetStream cluster on distinct Proxmox LXC guests.

LXC 511–513 (nats-a/b/c on 10.10.10.21–23, vmbr1 only) form cluster
verae with replicas=3. Host loopback 127.0.0.1:4222 is unchanged.

packages/verae-nats-cluster/conf/nats.conf.tmpl

@@ -0,0 +1,19 @@
+# JetStream cluster node. Bind the private guest IP only — never vmbr0 / 0.0.0.0.
+server_name: {{NAME}}
+host: {{IP}}
+port: 4222
+http: 127.0.0.1:8222
+
+jetstream {
+  store_dir: /var/lib/nats/jetstream
+  max_mem: 256M
+  max_file: 4G
+}
+
+cluster {
+  name: {{CLUSTER}}
+  listen: {{IP}}:6222
+  routes: [
+{{ROUTES}}
+  ]
+}