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/printing/default.nix

@@ -8,6 +8,21 @@ in
 {
   options.roles.printing = {
     enable = mkEnableOption "Enable default printing setup";
+    printerName = mkOption {
+      type = types.str;
+      default = "MFC-L8900CDW_series";
+      description = "Name for the default printer";
+    };
+    printerUri = mkOption {
+      type = types.str;
+      default = "ipp://brother.oglehome/ipp/print";
+      description = "Device URI for the default printer (e.g., ipp://hostname/ipp/print)";
+    };
+    printerModel = mkOption {
+      type = types.str;
+      default = "everywhere";
+      description = "PPD model for the printer (use 'everywhere' for driverless IPP)";
+    };
   };
 
   config = mkIf cfg.enable
@@ -21,11 +36,11 @@ in
       };
 
       hardware.printers.ensurePrinters = [{
-        name = "MFC-L8900CDW_series";
-        deviceUri = "ipp://brother.oglehome/ipp/print";
-        model = "everywhere";
+        name = cfg.printerName;
+        deviceUri = cfg.printerUri;
+        model = cfg.printerModel;
       }];
-      hardware.printers.ensureDefaultPrinter = "MFC-L8900CDW_series";
+      hardware.printers.ensureDefaultPrinter = cfg.printerName;
 
       # Fix ensure-printers service to wait for network availability
       systemd.services.ensure-printers = {