fix(desktop): correct dwindle keybinds and speed up the terminal

Two issues surfaced on the live neogaia session. Hyprland rejected two names
at load: the split toggle is a dwindle layout message reached through
layoutmsg, not a top-level dispatcher, and dwindle:pseudotile no longer exists
in this version. Bind Super+T via layoutmsg and drop the pseudotile option.

Ghostty also cold-started GTK on every launch. Configure it through
home-manager with gtk-single-instance so windows after the first open in the
existing process. Record the dispatcher/option version-drift trap in CLAUDE.md.

modules/desktop/terminal.nix

@@ -1,7 +1,6 @@
 {
   config,
   lib,
-  pkgs,
   ...
 }:
 # Ghostty as the desktop terminal.
@@ -13,6 +12,12 @@ in
   options.modules.desktop.terminal.enable = lib.mkEnableOption "Ghostty as the desktop terminal";
 
   config = lib.mkIf cfg.enable {
-    home-manager.users.${user}.home.packages = [ pkgs.ghostty ];
+    home-manager.users.${user}.programs.ghostty = {
+      enable = true;
+
+      # Reuse a single process, so each window after the first opens instantly
+      # instead of paying a fresh GTK startup.
+      settings.gtk-single-instance = true;
+    };
   };
 }