refactor(nixos): scope agent guidance

configs/nixos/modules/desktop/apps/firefox.nix

@@ -67,6 +67,8 @@ in
 
           # Stylix uses a near-white selection background.
           # Use the Nord selection color because its text stays readable.
+          # Home Manager writes extension settings through Firefox's legacy storage backend.
+          # Extension settings disable `ExtensionStorageIDB` for the whole profile.
           extensions.settings."FirefoxColor@mozilla.com".settings.theme.colors.popup_highlight =
             let
               c = hm.config.lib.stylix.colors;

configs/nixos/modules/shell/nvim/default.nix

@@ -24,6 +24,9 @@ in
     home-manager.users.${user} = hm: {
       programs.nixvim = {
         enable = true;
+
+        # Aligns Nixvim plugins with this flake's `Nixpkgs`.
+        # `nixpkgs.useGlobalPackages` prevents Home Manager from creating a separate package set.
         nixpkgs.useGlobalPackages = true;
 
         extraPackages = with pkgs; [