feat(sway): theme the ReGreet greeter to match (Catppuccin Mocha)

Factor the Catppuccin Mocha palette into lyrathorpe/catppuccin-mocha.nix
so the desktop (home/sway.nix) and the system greeter (swaywm.nix) share
one source of truth, then theme ReGreet from it: GTK CSS (libadwaita
named colours + plain node selectors for window/entry/button/combobox)
plus Noto Sans to match the bar and notifications.

Verified the rendered /etc/greetd/regreet.css and regreet.toml
(font_name = "Noto Sans 16"), and that foot still resolves its colours
through the shared import.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyrathorpe/home/sway.nix

@@ -15,31 +15,10 @@
   ...
 }:
 let
-  # Catppuccin Mocha. Raw 6-digit hex (no leading "#"); prefix "#" where a
-  # consumer needs it -- Sway/i3status/dunst want "#", foot/swaylock do not.
-  ctp = {
-    base = "1e1e2e";
-    mantle = "181825";
-    crust = "11111b";
-    surface0 = "313244";
-    surface1 = "45475a";
-    surface2 = "585b70";
-    overlay0 = "6c7086";
-    subtext0 = "a6adc8";
-    subtext1 = "bac2de";
-    text = "cdd6f4";
-    rosewater = "f5e0dc";
-    red = "f38ba8";
-    maroon = "eba0ac";
-    peach = "fab387";
-    yellow = "f9e2af";
-    green = "a6e3a1";
-    teal = "94e2d5";
-    sapphire = "74c7ec";
-    blue = "89b4fa";
-    mauve = "cba6f7";
-    pink = "f5c2e7";
-  };
+  # Catppuccin Mocha (shared with the ReGreet greeter). Raw hex; prefix "#"
+  # where a consumer needs it -- Sway/i3status/dunst want "#", foot/swaylock do
+  # not.
+  ctp = import ../catppuccin-mocha.nix;
 in
 {
   wayland.windowManager.sway = {