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.

agent/MEMORY.md

@@ -10,14 +10,12 @@ iteration would otherwise rediscover.
 - **Doctor float V2:** `THEME=<slug> nix build --impure -f tools/doctor-float.nix`
   — softGL Hyprland, `nomarchy-menu doctor`, asserts
   `class=com.nomarchy.doctor` + `floating` + centered midpoints +
-  screenshots. Ghostty *does* start here under softGL (classed one-shot);
-  size often stays Ghostty’s default 800×600 (client geometry wins over
-  the percent `size` windowrule).
-- **theme-shot softGL cannot start Ghostty** — `btop.png` is best-effort
+  screenshots (Kitty `--class=…`). SoftGL may still struggle with a GPU
+  terminal; size can ignore percent windowrules if client geometry wins.
+- **theme-shot softGL may not start Kitty** — `btop.png` is best-effort
   (usually identical to desktop). Guest asserts on
   `~/.config/btop/themes/nomarchy.theme` prove baking; the TUI look is
-  hardware/GL tier (HARDWARE-QUEUE). Doctor float is the counter-example
-  that a *classed* one-shot Ghostty can still map under softGL.
+  hardware/GL tier (HARDWARE-QUEUE).
 - **Waybar `custom/doctor` tripwire:** status helper must invoke
   `nomarchy-doctor` by **absolute store path** (waybar's env can miss
   system PATH → `command -v … || exit 0` self-hides forever); empty
@@ -85,9 +83,9 @@ iteration would otherwise rediscover.
   (`LIBGL_ALWAYS_SOFTWARE` on virtio-gpu) + `machine.screenshot()` QMP
   dump — prototyped 2026-06-19, kept as the fallback for theme previews
   (§ Visual theme picker).
-- Hyprland/Ghostty need guest GL (`virtio-vga-gl`, `gl=on`) in
-  interactive QEMU or the session won't start; black screen ≈ missing GL
-  (docs/TESTING.md § gotchas).
+- Hyprland needs guest GL (`virtio-vga-gl`, `gl=on`) in interactive QEMU
+  or the session won't start; black screen ≈ missing GL
+  (docs/TESTING.md § gotchas). Kitty is the sole terminal (no Ghostty).
 - No KVM = slow, not broken; don't read slowness as failure.
 
 ## Known-broken / watchlist