flakes: Migrate the config and miku to flakes

modules/programs/git/default.nix

@@ -1,9 +1,14 @@
-{ config, pkgs, ... }:
+{ config, lib, pkgs, ... }:
 
-{
-  config = {
+let
+  cfg = config.ptw.programs.git;
+in {
+  options.ptw.programs.git = {
+    enable = lib.mkEnableOption "Configure git using HomeManager";
+  };
+  config = lib.mkIf cfg.enable {
     environment.systemPackages = [ pkgs.diff-so-fancy ];
-    home-manager.users."${config.system.singleUser}".programs.git = {
+    home-manager.users."${config.ptw.system.singleUser}".programs.git = {
       enable = true;
       userEmail = "papatutuwawa@polynom.me";
       userName = "Alexander \"PapaTutuWawa\"";