homelab-deploy: enable prometheus metrics

- Update homelab-deploy input to get metrics support
- Enable metrics endpoint on port 9972
- Add scrape target for prometheus auto-discovery

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

flake.lock

@@ -28,11 +28,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1770443536,
-        "narHash": "sha256-UufZIVggiioMFDSjKx+ifgkDOk9alNSiRmkvc4/+HIA=",
+        "lastModified": 1770447502,
+        "narHash": "sha256-xH1PNyE3ydj4udhe1IpK8VQxBPZETGLuORZdSWYRmSU=",
         "ref": "master",
-        "rev": "95b795dcfd86b7b36045bba67e536b3a1c61dd33",
-        "revCount": 20,
+        "rev": "79db119d1ca6630023947ef0a65896cc3307c2ff",
+        "revCount": 22,
         "type": "git",
         "url": "https://git.t-juice.club/torjus/homelab-deploy"
       },