refactor: migrate nix-darwin config to a flake-parts dendritic layout

modules/aspects/activation.nix

@@ -0,0 +1,31 @@
+{...}: {
+  flake.modules.darwin.activation = {
+    config,
+    lib,
+    pkgs,
+    ...
+  }: {
+    system.activationScripts.extraActivation.text = ''
+      sudo -u ${config.repo.user.name} /System/Library/PrivateFrameworks/SystemAdministration.framework/Resources/activateSettings -u
+    '';
+
+    system.activationScripts.applications.text = let
+      env = pkgs.buildEnv {
+        name = "system-applications";
+        paths = config.environment.systemPackages;
+        pathsToLink = ["/Applications"];
+      };
+    in
+      lib.mkForce ''
+        echo "setting up /Applications..." >&2
+        rm -rf /Applications/Nix\ Apps
+        mkdir -p /Applications/Nix\ Apps
+        find ${env}/Applications -maxdepth 1 -type l -exec readlink '{}' + |
+        while read -r src; do
+          app_name=$(basename "$src")
+          echo "copying $src" >&2
+          ${pkgs.mkalias}/bin/mkalias "$src" "/Applications/Nix Apps/$app_name"
+        done
+      '';
+  };
+}