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/shell.nix

@@ -1,11 +1,11 @@
 # Shell experience — zsh (the default login shell, set system-side) with
 # autosuggestions + syntax highlighting, a themed starship prompt, and
 # modern CLI tools wired in: bat (cat), eza (ls), zoxide (cd). bat uses
-# the "ansi" theme so it follows the terminal palette (Ghostty is themed
+# the "ansi" theme so it follows the terminal palette (Kitty is themed
 # from the same JSON); starship is themed from the palette directly.
 #
 # home.shell.enableZshIntegration = true is the single lever that makes
-# every integrating program (starship, eza, zoxide, ghostty, yazi) emit
+# every integrating program (starship, eza, zoxide, kitty, yazi) emit
 # its zsh hooks — no per-module flags needed.
 { config, lib, pkgs, ... }:
 
@@ -133,7 +133,7 @@ in
     };
 
     # bat: "ansi" follows the terminal's 16-color palette → tracks the
-    # active Nomarchy theme (Ghostty bakes it) with no per-theme config.
+    # active Nomarchy theme (Kitty bakes it) with no per-theme config.
     programs.bat = {
       enable = true;
       config = {