fix(desktop): switch the terminal from Ghostty to Alacritty

Ghostty's GTK4 window construction made every launch sluggish on neogaia's
integrated graphics (~440 ms to map a window), which a head-to-head
comparison against Alacritty confirmed. Alacritty's lightweight OpenGL
renderer opens fast on the iGPU, so it becomes the terminal on Super+Return.

The choice stays reversible per host, so a capable host such as zeus could
adopt Ghostty later.

modules/desktop/hyprland/hyprland.nix

@@ -50,7 +50,7 @@ in
 
       settings = {
         "$mod" = "SUPER";
-        "$terminal" = "ghostty";
+        "$terminal" = "alacritty";
 
         input = {
           kb_layout = "us";