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/mediamanager.json

@@ -0,0 +1,45 @@
+{
+  "name": "MediaManager",
+  "slug": "mediamanager",
+  "categories": [
+    14,
+    13
+  ],
+  "date_created": "2025-08-28",
+  "type": "ct",
+  "updateable": true,
+  "privileged": false,
+  "interface_port": 8000,
+  "documentation": "https://maxdorninger.github.io/MediaManager/latest/",
+  "config_path": "/opt/mm/config/config.toml",
+  "website": "https://github.com/maxdorninger/MediaManager",
+  "logo": "https://cdn.jsdelivr.net/gh/selfhst/icons@main/webp/mediamanager.webp",
+  "description": "A modern selfhosted media management system for your media library",
+  "install_methods": [
+    {
+      "type": "default",
+      "script": "ct/mediamanager.sh",
+      "resources": {
+        "cpu": 2,
+        "ram": 3072,
+        "hdd": 4,
+        "os": "Debian",
+        "version": "13"
+      }
+    }
+  ],
+  "default_credentials": {
+    "username": "<email address>",
+    "password": "admin"
+  },
+  "notes": [
+    {
+      "text": "During the installation, provide the email address of the first admin user",
+      "type": "info"
+    },
+    {
+      "text": "You're probably going to want to use a bind mount for the media directories",
+      "type": "info"
+    }
+  ]
+}