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/options.nix

@@ -100,17 +100,17 @@ in
     # ── Preferences ────────────────────────────────────────────────
     terminal = lib.mkOption {
       type = lib.types.str;
-      default = config.nomarchy.settings.terminal or "ghostty";
+      default = config.nomarchy.settings.terminal or "kitty";
       example = "kitty";
       description = ''
-        Terminal emulator command, used by keybinds and `$TERMINAL`.
-        Default is Ghostty. On GPUs below OpenGL 4.3 the installer writes
-        `settings.terminal = "kitty"` so SUPER+Return still works (Ghostty
-        needs 4.3; see docs/REQUIREMENTS.md). Set explicitly to override.
+        Terminal emulator command for keybinds and `$TERMINAL`. Nomarchy
+        ships and themes **Kitty only** (sole supported terminal — works
+        on older GPUs that Ghostty's OpenGL 4.3 floor rejected). Override
+        only if you install another emulator yourself.
       '';
     };
 
-    kitty.enable = lib.mkEnableOption "Kitty with Nomarchy theming (palette/font/opacity from theme-state); also auto-on when nomarchy.terminal is kitty (OpenGL < 4.3 install fallback)";
+    kitty.enable = lib.mkEnableOption "Nomarchy's Kitty configuration (palette/font/opacity from theme-state)" // { default = true; };
 
     keyboard.layout = lib.mkOption {
       type = lib.types.str;
@@ -403,7 +403,6 @@ in
     shell.enable = lib.mkEnableOption "the zsh shell experience (starship prompt, bat/eza/zoxide)" // { default = true; };
     keys.enable = lib.mkEnableOption "the SSH + GPG agent (gpg-agent fronting SSH, pinentry-qt)" // { default = true; };
     fastfetch.enable = lib.mkEnableOption "fastfetch system info fronted by the themed Nomarchy logo" // { default = true; };
-    ghostty.enable = lib.mkEnableOption "Nomarchy's Ghostty configuration" // { default = true; };
     btop.enable = lib.mkEnableOption "btop with the per-theme nomarchy theme" // { default = true; };
     stylix.enable = lib.mkEnableOption "Stylix theming for the long tail of apps (GTK, Qt, cursors)" // { default = true; };
     displays.enable = lib.mkEnableOption "the nwg-displays interactive monitor arranger (a helper to find nomarchy.monitors values; the declarative config stays the source of truth)" // { default = true; };