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.

modules/nixos/default.nix

@@ -4,7 +4,7 @@
 # nixosModules.nomarchy in flake.nix) and layer your machine specifics
 # (bootloader, hostname, users, hardware) on top. Host concerns are
 # deliberately NOT set here. Everything user-facing (Hyprland config,
-# Waybar, Ghostty, theming) lives in modules/home.
+# Waybar, Kitty, theming) lives in modules/home.
 { config, lib, pkgs, ... }:
 
 let