feat(terminal): themed Kitty when OpenGL < 4.3 (#95)

Ghostty needs OpenGL 4.3; older GPUs (Intel HD 4000) top out at 4.2.
Installer probes glxinfo and writes settings.terminal=kitty into
theme-state when below the floor. modules/home/kitty.nix enables Kitty
with the same palette, mono font, and opacity as Ghostty so the fallback
still looks like Nomarchy.

Default machines stay Ghostty-only (no kitty in the HM closure). Doctor
and calendar still invoke Ghostty by class — V3 on Acer for SUPER+Return.

Verified: V0 flake check; installer-safety; HM with terminal=kitty builds
themed kitty.conf + TERMINAL=kitty; default template has no kitty bin.

templates/downstream/home.nix

@@ -14,7 +14,10 @@
   nomarchy.keyboard.variant = "";
 
   # ── Overrides (the desktop is on by default; tweak or opt out) ──────
-  # nomarchy.terminal = "kitty";        # swap the default terminal
+  # 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.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