fix(ghostty): add cairo wrapper and make it the default terminal

modules/system/packages.nix

@@ -1,5 +1,11 @@
 { lib, pkgs, ... }:
 
+let
+  ghosttyCairo = pkgs.writeShellScriptBin "ghostty-cairo" ''
+    export GSK_RENDERER=cairo
+    exec ghostty "$@"
+  '';
+in
 {
   # Baseline system tools available everywhere; users run Home Manager standalone.
   config.environment.systemPackages = lib.mkAfter [
@@ -11,6 +17,7 @@
     pkgs.fastfetch
     pkgs.flatpak
     pkgs.ghostty
+    ghosttyCairo
     pkgs.git
     pkgs.home-manager
     pkgs.just