moved home manager user configuration to dedicated files

aspects/users/user_rotterdam.nix

@@ -0,0 +1,35 @@
+{ inputs, lib, ... }:
+
+{
+  flake.homeConfigurations = {
+    "user@rotterdam" = inputs.home-manager.lib.homeManagerConfiguration {
+      pkgs = inputs.nixpkgs.legacyPackages.x86_64-linux;
+      extraSpecialArgs = {
+        inherit inputs;
+        hostname = "rotterdam";
+      };
+      modules = [
+        { nixpkgs.overlays = [ inputs.self.overlays.default ]; }
+        {
+          home = {
+            username = "user";
+            homeDirectory = "/home/user";
+            stateVersion = "22.05";
+          };
+        }
+        ((inputs.import-tree.initFilter (p: lib.hasSuffix ".nix" p)) ./_user)
+      ]
+      ++ (with inputs.self.modules.homeManager; [
+        # system aspects
+        base
+        cli
+        desktop
+        gaming
+
+        # other aspects
+        stylix
+        niri
+      ]);
+    };
+  };
+}