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.

templates/downstream/home.nix

@@ -1,5 +1,5 @@
 # Your user environment. The Nomarchy desktop (Hyprland, Waybar,
-# Ghostty, theming engine, Stylix) comes from homeModules.nomarchy;
+# Kitty, theming engine, Stylix) comes from homeModules.nomarchy;
 # tune it via the nomarchy.* options, add your own packages and
 # programs below.
 #
@@ -14,10 +14,8 @@
   nomarchy.keyboard.variant = "";
 
   # ── Overrides (the desktop is on by default; tweak or opt out) ──────
-  # nomarchy.terminal = "kitty";        # swap the default terminal (installer
-  #                                     # sets this via settings.terminal when
-  #                                     # OpenGL < 4.3 — Ghostty needs 4.3)
-  # nomarchy.kitty.enable = true;       # themed Kitty without making it default
+  # nomarchy.terminal = "kitty";        # default; only Kitty is shipped/themed
+  # nomarchy.kitty.enable = false;      # keep the package, drop our config
   # nomarchy.waybar.enable = false;     # bring your own bar
   # nomarchy.stylix.enable = false;     # opt out of GTK/Qt theming
   # nomarchy.dockAudio.enable = false;  # keep audio put when docking