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.

docs/ROADMAP.md

@@ -404,12 +404,13 @@ Design/decision records and a running log of shipped work (items marked
   decision rather than a drive-by. Proved to fail: dropping snapshot makes it
   name the missing entry. **V3 pending** — that the apps *launch* needs real
   hardware (HARDWARE-QUEUE, Acer M5-481T).
-- ✓ **Kitty fallback when OpenGL < 4.3 (#95 partial):** Ghostty needs GL 4.3;
-  Ivy Bridge HD 4000 tops at 4.2 (Acer M5-481T). Installer probes `glxinfo`
-  and writes `settings.terminal = "kitty"` when below the floor; `kitty.nix`
-  themes Kitty from the same theme-state as Ghostty (ANSI, mono font,
-  opacity). Default machines stay Ghostty-only in the HM closure. V3 on Acer
-  still needed; doctor/calendar still invoke Ghostty by class.
+- ✓ **Kitty is the only terminal (#95 complete):** Ghostty’s OpenGL 4.3 floor
+  broke SUPER+Return (and classed doctor/calendar windows) on Ivy Bridge
+  HD 4000 (Acer M5-481T). Maintaining two terminals was pure complexity.
+  **Kitty only:** always installed, themed from theme-state (ANSI/font/opacity),
+  default `$TERMINAL` / SUPER+Return, doctor + calendar + what-changed use
+  `kitty --class=com.nomarchy.*`. Ghostty module and install-time GL probe
+  removed. V3: Acer SUPER+Return + doctor float.
 - ✓ **Mime defaults must name a present .desktop (#119):** same bug class as
   #94, one key over. `text/plain` pointed at `code.desktop` (vscode), which
   the live ISO never ships — GIO skips the missing entry and leaves no