homelab-deploy: add NATS-based deployment system

Add homelab-deploy flake input and NixOS module for message-based
deployments across the fleet. Configure DEPLOY account in NATS with
tiered access control (listener, test-deployer, admin-deployer).
Enable listener on vaulttest01 as initial test host.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.lock

@@ -21,6 +21,27 @@
         "url": "https://git.t-juice.club/torjus/alerttonotify"
       }
     },
+    "homelab-deploy": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs-unstable"
+        ]
+      },
+      "locked": {
+        "lastModified": 1770437282,
+        "narHash": "sha256-7C6hheIP8JUkK0Aoib/lQ4xbOaXHoqSe9SJjU2u3t/Q=",
+        "ref": "master",
+        "rev": "cf3b1ce2c9e85ad954d8c230161553c5473e9579",
+        "revCount": 12,
+        "type": "git",
+        "url": "https://git.t-juice.club/torjus/homelab-deploy"
+      },
+      "original": {
+        "ref": "master",
+        "type": "git",
+        "url": "https://git.t-juice.club/torjus/homelab-deploy"
+      }
+    },
     "labmon": {
       "inputs": {
         "nixpkgs": [
@@ -97,6 +118,7 @@
     "root": {
       "inputs": {
         "alerttonotify": "alerttonotify",
+        "homelab-deploy": "homelab-deploy",
         "labmon": "labmon",
         "nixos-exporter": "nixos-exporter",
         "nixpkgs": "nixpkgs",