feat(terminal): Kitty only — drop Ghostty (#95)

Ghostty's OpenGL 4.3 floor broke the Acer (HD 4000 / 4.2). Dual-terminal
support (default Ghostty + install-time Kitty fallback) was more complexity
than it was worth.

- Remove ghostty.nix / nomarchy.ghostty.enable
- Kitty always installed and themed from theme-state
- Default nomarchy.terminal = kitty; SUPER+Return, doctor, calendar,
  what-changed use kitty --class=com.nomarchy.*
- Drop install-time glxinfo probe and mesa-demos on the installer
- Docs/REQUIREMENTS no longer list OpenGL 4.3 as a terminal floor

Verified: V0 flake check; option-docs; installer-safety; template HM has
kitty, no ghostty; menu/calendar emit classed kitty launches.

pkgs/nomarchy-control-center/nomarchy-control-center.sh

@@ -211,12 +211,9 @@ function toggles_menu() {
                 sleep 1
                 ;;
             "Terminal")
-                term=$(gum choose "ghostty" "kitty" "alacritty" "wezterm" "foot")
-                if [ -n "$term" ]; then
-                    set_state "settings.terminal" "\"$term\""
-                    echo "Terminal set to $term (requires rebuild)."
-                fi
-                sleep 1
+                echo "Kitty is Nomarchy's terminal (themed from theme-state)."
+                echo "Override nomarchy.terminal in home.nix only if you install another yourself."
+                sleep 2
                 ;;
             "Keyboard Layout")
                 layout=$(gum input --prompt "Enter keyboard layout (e.g. us, de, es): " --placeholder "$(get_state settings.keyboard.layout | tr -d '"')")