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-theme-sync/nomarchy-theme-sync.py

@@ -6,7 +6,7 @@ read purely by Home Manager via the nomarchy.stateFile option).
 
 Theme changes are applied by Home Manager: this tool writes the new state
 and runs `home-manager switch` (override with $NOMARCHY_REBUILD, or skip
-with --no-switch). All app theming — Hyprland, Waybar, Ghostty, btop,
+with --no-switch). All app theming — Hyprland, Waybar, Kitty, btop,
 Stylix — is baked into the generation; nothing is patched at runtime.
 
 The one runtime exception is the wallpaper: swww is imperative by nature,