refactor(flake-parts): initial flake-parts configuration

inputs/system/modules/base/bootloader/plymouth/default.nix

@@ -0,0 +1,15 @@
+{ lib, config, pkgs, ... }:
+
+let
+  cfg = config.systemModules.plymouth;
+in
+
+{
+  config = lib.mkIf cfg.enable {
+    boot.plymouth = {
+      enable = true;
+      themePackages = [(pkgs.catppuccin-plymouth.override {variant = "mocha";})];
+      theme = "catppuccin-mocha";
+    };
+  };
+}