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-install/default.nix

@@ -15,7 +15,6 @@
 , pciutils         # lspci
 , usbutils         # lsusb (fingerprint-reader VID probe; sysfs is the fallback)
 , btrfs-progs      # inspect-internal map-swapfile (hibernation offset)
-, mesa-demos       # glxinfo — OpenGL probe for Ghostty floor (needs 4.3)
 , xkeyboard_config # human-readable installed layout/variant catalog
   # Baked metadata — what this installer installs and where it came from.
 , templateDir              # templates/downstream (home.nix, theme-state.json)
@@ -65,7 +64,6 @@ stdenvNoCC.mkDerivation {
       --prefix PATH : ${lib.makeBinPath [
         bash gum disko whois git python3
         util-linux gptfdisk parted cryptsetup lvm2 pciutils usbutils btrfs-progs
-        mesa-demos
       ]} \
       --set NOMARCHY_INSTALL_SHARE "$share" \
       --set NOMARCHY_XKB_RULES ${xkeyboard_config}/share/X11/xkb/rules/base.lst \