feat: set helix as default editor

modules/capabilities/helix.nix

@@ -31,6 +31,7 @@
     {
       programs.helix = {
         enable = true;
+        defaultEditor = true;
         package = inputs.helix.packages.${pkgs.stdenv.hostPlatform.system}.default;
         extraPackages = with pkgs; [
           svelteLanguageServer