Update flake.lock and kemptop configuration

Use pkgs.linuxPackages instead of linuxPackages_latest for
kernelPackages.
Enable the system firewall (networking.firewall.enable = true).
Comment out users.groups.kemp members entry.
Add jdk and gradle to environment.systemPackages.
Enable VirtualBox host and extension pack and add kemp to vboxusers.

flake.lock

@@ -65,11 +65,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1771492583,
-        "narHash": "sha256-nQzvnU4BGu8dA6BsPPCqmVcab/3ebVmHtX3ZWbW3Hxc=",
+        "lastModified": 1771834715,
+        "narHash": "sha256-5VI2KiMifx3Dca7nDJzctO3HpnS6zrvesdkLoZBrQRY=",
         "owner": "nix-community",
         "repo": "lanzaboote",
-        "rev": "5e9380994665ef66c87ab8e22c913ff837174ce4",
+        "rev": "b798c53da0f7e521317a5413335096a21070cf0b",
         "type": "github"
       },
       "original": {
@@ -95,11 +95,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1771369470,
-        "narHash": "sha256-0NBlEBKkN3lufyvFegY4TYv5mCNHbi5OmBDrzihbBMQ=",
+        "lastModified": 1771848320,
+        "narHash": "sha256-0MAd+0mun3K/Ns8JATeHT1sX28faLII5hVLq0L3BdZU=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "0182a361324364ae3f436a63005877674cf45efb",
+        "rev": "2fc6539b481e1d2569f25f8799236694180c0993",
         "type": "github"
       },
       "original": {
@@ -147,11 +147,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1771729765,
-        "narHash": "sha256-HNsDSR5bhLSrIpi9bTb2uTK1qnPo1xFSBxs6YmFyprk=",
+        "lastModified": 1771902481,
+        "narHash": "sha256-svI5ivzggtu4KhCdoab3xR5+Btop24o7yLFtIPXrsPM=",
         "owner": "oxalica",
         "repo": "rust-overlay",
-        "rev": "be926cb1a76e8450ab2b92121b2e88d09fa4d41c",
+        "rev": "5177426d9f8f7f1827001c9749b9a9c5570d456b",
         "type": "github"
       },
       "original": {