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/kernel-clean.json

@@ -0,0 +1,40 @@
+{
+  "name": "PVE Kernel Clean",
+  "slug": "kernel-clean",
+  "categories": [
+    1
+  ],
+  "date_created": "2024-04-29",
+  "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": "Cleaning unused kernel images is beneficial for reducing the length of the GRUB menu and freeing up disk space. By removing old, unused kernels, the system is able to conserve disk space and streamline the boot process.",
+  "install_methods": [
+    {
+      "type": "default",
+      "script": "tools/pve/kernel-clean.sh",
+      "resources": {
+        "cpu": null,
+        "ram": null,
+        "hdd": null,
+        "os": null,
+        "version": null
+      }
+    }
+  ],
+  "default_credentials": {
+    "username": null,
+    "password": null
+  },
+  "notes": [
+    {
+      "text": "Execute within the Proxmox shell",
+      "type": "info"
+    }
+  ]
+}