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/yazi.nix

@@ -1,5 +1,5 @@
 # yazi — the flagship file manager: a fast, keyboard-driven TUI that
-# fits the distro's identity (Ghostty's Kitty-graphics previews, rofi
+# fits the distro's identity (Kitty graphics previews, rofi
 # menus, everything from one JSON). Themed from theme-state.json and
 # shipped with a curated plugin set. The GUI half (Thunar, "open folder"
 # handler) is nomarchy.system.fileManager on the system side.
@@ -92,7 +92,7 @@ in
 
       # Theme from the palette. yazi merges this over its built-in theme,
       # so only the accent-bearing UI is specified; everything else keeps
-      # yazi's defaults (which already follow Ghostty's ANSI colors).
+      # yazi's defaults (which already follow Kitty's ANSI colors).
       theme = {
         mgr = {
           cwd = { fg = c.accent; };