feat(roles): Parameterize hardcoded values in printing, nfs-mounts, and virtualisation roles

- printing role: Add configurable printerName, printerUri, and printerModel options
  to replace hardcoded Brother printer values
- nfs-mounts role: Add configurable server, remotePath, and mountPoint options
  to replace hardcoded NFS server IP (10.0.0.43)
- virtualisation role: Add configurable dockerUsers option as list type
  to replace hardcoded 'johno' docker group membership

All options have sensible defaults matching the original hardcoded values,
ensuring backward compatibility while allowing per-host customization.

Implements bead: nixos-configs-fkt

roles/nfs-mounts/default.nix

@@ -8,6 +8,21 @@ in
 {
   options.roles.nfs-mounts = {
     enable = mkEnableOption "Enable default NFS mounts";
+    server = mkOption {
+      type = types.str;
+      default = "10.0.0.43";
+      description = "IP address or hostname of the NFS server";
+    };
+    remotePath = mkOption {
+      type = types.str;
+      default = "/media";
+      description = "Remote path to mount from the NFS server";
+    };
+    mountPoint = mkOption {
+      type = types.str;
+      default = "/media";
+      description = "Local mount point for the NFS share";
+    };
     # TODO: implement requireMount
     requireMount = mkOption {
       type = types.bool;
@@ -18,8 +33,8 @@ in
 
   config = mkIf cfg.enable
     {
-      fileSystems."/media" = {
-        device = "10.0.0.43:/media";
+      fileSystems.${cfg.mountPoint} = {
+        device = "${cfg.server}:${cfg.remotePath}";
         fsType = "nfs";
         options = [
           "defaults"