treewide: move defaults to dedicated folder

defaults/git.nix

@@ -0,0 +1,47 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+
+let
+  name = "git";
+  cfg = config.nixowos.cli.${name};
+in
+{
+  options.nixowos.cli.${name} = {
+    enable = lib.mkEnableOption name;
+
+    delta.enable = lib.mkEnableOption "delta within git" // {
+      default = true;
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+
+    programs.git = {
+      enable = true;
+
+      config = lib.mkMerge [
+        {
+          init.defaultBranch = "main";
+          core.compression = 9; # max
+          credential.helper = "cache";
+
+          push.autoSetupRemote = true;
+          pull.ff = "only";
+          merge.conflictStyle = "zdiff3";
+          commit.verbose = true; # show diffs in commit editor
+        }
+        (lib.mkIf cfg.delta.enable {
+          core.pager = "${pkgs.delta}/bin/delta";
+          interactive.diffFilter = "${pkgs.delta}/bin/delta --color-only";
+          delta.navigate = true; # use n and N to move between diff sections
+          delta.diff-highlight = true; # simpler mode, highlights inter-line changes
+        })
+      ];
+    };
+
+  };
+}