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.

tools/test-live-iso.sh

@@ -39,7 +39,7 @@ ACCEL_ARG=()
 
 echo "Launching ISO: $ISO"
 # virtio-vga-gl + gl=on gives the guest real OpenGL — Hyprland and
-# Ghostty need it; without GL the session may fail to start.
+# the session needs it; without GL Hyprland may fail to start.
 exec qemu-system-x86_64 \
     "${ACCEL_ARG[@]}" \
     -m 4096 -smp 2 \