waybar: use catppuccin module, add GTK theme

Switch waybar from manual fetchFromGitHub theme to catppuccin/nix module.
Add catppuccin macchiato GTK theme to fix unreadable tray context menus.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

home/programs/gtk/default.nix

@@ -0,0 +1,13 @@
+{ pkgs, ... }:
+{
+  gtk = {
+    enable = true;
+    theme = {
+      name = "catppuccin-macchiato-blue-standard";
+      package = pkgs.catppuccin-gtk.override {
+        variant = "macchiato";
+        accents = [ "blue" ];
+      };
+    };
+  };
+}