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.

docs/OVERRIDES.md

@@ -11,7 +11,7 @@ rule of thumb:
 
 Everything that defines the *look* flows from `theme-state.json`, the single
 source of truth. Change it with `nomarchy-theme-sync`, which writes the JSON
-and rebuilds — one generation, applied to Hyprland, Waybar, Ghostty, btop and
+and rebuilds — one generation, applied to Hyprland, Waybar, Kitty, btop and
 Stylix at once:
 
 ```sh
@@ -98,9 +98,8 @@ in your `home.nix` wins — no `mkForce` needed:
     animations.enabled = false;
   };
 
-  programs.ghostty.settings = {
-    window-padding-x = 4;              # was 12
-    window-decoration = true;
+  programs.kitty.settings = {
+    window_padding_width = 4;          # was 12
   };
 }
 ```