template2: add filesystem definitions to support normal builds

Add filesystem configuration matching Proxmox image builder output
to allow template2 to build with both `nixos-rebuild build` and
`nixos-rebuild build-image --image-variant proxmox`.

Filesystem specs discovered from running VM:
- ext4 filesystem with label "nixos"
- x-systemd.growfs option for automatic partition growth
- No swap partition

Using lib.mkDefault ensures these definitions work for normal builds
while allowing the Proxmox image builder to override when needed.

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

hosts/template2/hardware-configuration.nix

@@ -25,6 +25,15 @@
   ];
   boot.extraModulePackages = [ ];
 
+  # Filesystem configuration matching Proxmox image builder output
+  fileSystems."/" = lib.mkDefault {
+    device = "/dev/disk/by-label/nixos";
+    fsType = "ext4";
+    options = [ "x-systemd.growfs" ];
+  };
+
+  swapDevices = lib.mkDefault [ ];
+
   # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
   # (the default) this is the recommended approach. When using systemd-networkd it's
   # still possible to use this option, but it's recommended to use it in conjunction