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/home/default.nix

@@ -10,8 +10,7 @@
     ./stylix.nix    # GTK/Qt/cursor/fonts from the same JSON
     ./hyprland.nix
     ./waybar.nix
-    ./ghostty.nix
-    ./kitty.nix     # themed fallback when Ghostty cannot run (OpenGL < 4.3)
+    ./kitty.nix     # sole terminal (themed); doctor/calendar/--class load-bearing
     ./btop.nix
     ./rofi.nix      # launcher theming + the nomarchy-menu dispatcher
     ./swaync.nix    # notification daemon, themed from the same JSON