Move common nix code one level up.

common/global/default.nix

@@ -0,0 +1,25 @@
+{ pkgs, self, ... }:
+{
+  imports = [
+    ./cpufreq.nix
+    ./flakes.nix
+    ./locale.nix
+    ./network.nix
+    ./nix.nix
+    ./packages.nix
+    ./sudo.nix
+    ./tailscale.nix
+  ];
+
+  system.copySystemConfiguration = false; # not supported with flakes
+  # Let 'nixos-version --json' know about the Git revision of the flake
+  system.configurationRevision = pkgs.lib.mkIf (self ? rev) self.rev;
+
+  # This value determines the NixOS release from which the default
+  # settings for stateful data, like file locations and database versions
+  # on your system were taken. It's perfectly fine and recommended to leave
+  # this value at the release version of the first install of this system.
+  # Before changing this value read the documentation for this option
+  # (e.g. man configuration.nix or on https://nixos.org/nixos/options.html).
+  system.stateVersion = "23.05"; # Did you read the comment?
+}