refactor: remove frontend, move JSONs to json/ top-level

- Archive frontend to community-scripts/ProxmoxVE-Frontend-Archive
- Move frontend/public/json/ -> json/
- Update workflow paths in 5 actions:
  - update-versions-github.yml
  - update-json-date.yml
  - push-json-to-pocketbase.yml
  - delete-pocketbase-entry-on-removal.yml
  - autolabeler.yml
- Remove frontend-cicd.yml (no longer needed)
- Clean up .gitignore (remove frontend-specific entries)

json/post-pmg-install.json

@@ -0,0 +1,48 @@
+{
+  "name": "PMG Post Install",
+  "slug": "post-pmg-install",
+  "categories": [
+    1
+  ],
+  "date_created": "2025-01-20",
+  "type": "pve",
+  "updateable": false,
+  "privileged": false,
+  "interface_port": null,
+  "documentation": null,
+  "website": null,
+  "logo": "https://cdn.jsdelivr.net/gh/selfhst/icons@main/webp/proxmox.webp",
+  "config_path": "",
+  "description": "The script is designed for Proxmox Mail Gateway and will give options to Disable the Enterprise Repo, Add/Correct PMG Sources, Enable the No-Subscription Repo, Add Test Repo, Disable Subscription Nag, Update Proxmox Mail Gateway and Reboot PMG.",
+  "install_methods": [
+    {
+      "type": "default",
+      "script": "tools/pve/post-pmg-install.sh",
+      "resources": {
+        "cpu": null,
+        "ram": null,
+        "hdd": null,
+        "os": null,
+        "version": null
+      }
+    }
+  ],
+  "default_credentials": {
+    "username": null,
+    "password": null
+  },
+  "notes": [
+    {
+      "text": "Proxmox Mail Gateway ONLY",
+      "type": "warning"
+    },
+    {
+      "text": "Execute within the Proxmox Mail Gateway Shell",
+      "type": "info"
+    },
+    {
+      "text": "It is recommended to answer “yes” (y) to all options presented during the process.",
+      "type": "info"
+    }
+  ]
+}