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/waybar.nix

@@ -93,20 +93,15 @@ let
     [ -n "$next" ] && powerprofilesctl set "$next"
   '';
 
-  # Opens calcurse (a lightweight TUI calendar, month view by default) in a
-  # floating, centered ghostty window — bound to the Waybar clock's on-click.
-  # A distinct --class gives the window a matchable app-id for the
-  # float+center+size windowrule (hyprland.nix); --gtk-single-instance=false
-  # forces a fresh standalone window (ghostty defaults single-instance on).
-  # calcurse is installed with the bar (home.packages below); the gate is
-  # only for someone who force-removed it. ghostty is always installed
-  # (ghostty.nix), so it can be relied on for the --class window.
+  # Opens calcurse (lightweight TUI calendar) in a floating, centered kitty
+  # window — Waybar clock on-click. Distinct --class → hyprland.nix float
+  # rules. Kitty is always installed (kitty.nix).
   calendarLauncher = pkgs.writeShellScriptBin "nomarchy-calendar" ''
     if ! command -v calcurse >/dev/null 2>&1; then
       notify-send "Calendar" "calcurse isn't installed (removed from home.packages?)." 2>/dev/null
       exit 0
     fi
-    exec ghostty --class=com.nomarchy.calendar --gtk-single-instance=false -e calcurse
+    exec kitty --class=com.nomarchy.calendar -e calcurse
   '';
 
   # VPN indicator — shows a shield when a NetworkManager VPN/WireGuard
@@ -213,7 +208,7 @@ let
       # into clock + clock#date — one click surface for the calendar).
       format = "{:%H:%M  ·  %a %d %b}";
       # Left-click → the calendar (nomarchy-calendar → calcurse in a floating
-      # ghostty). Tooltip is plain date/zone only — embedding {calendar}
+      # kitty). Tooltip is plain date/zone only — embedding {calendar}
       # produced an empty popup on hardware (2026-07-10); month view is
       # one click away.
       on-click = "nomarchy-calendar";