fix: avoid mkForce for allowUnfree and boot timeout (#355)

Let hosts override these again and drop the forced priorities.

modules/nixos/base/nix.nix

@@ -8,7 +8,7 @@
   # nix.package = pkgs.lix;
 
   # to install chrome, you need to enable unfree packages
-  nixpkgs.config.allowUnfree = lib.mkForce true;
+  nixpkgs.config.allowUnfree = lib.mkDefault true;
 
   # do garbage collection weekly to keep disk usage low
   nix.gc = {

modules/nixos/desktop/misc.nix

@@ -4,7 +4,9 @@
   ...
 }:
 {
-  boot.loader.timeout = lib.mkForce 10; # wait for x seconds to select the boot entry
+  # Normal priority on purpose: it must beat the base module's
+  # `lib.mkDefault 8` without forcing (two mkDefault definitions would conflict).
+  boot.loader.timeout = 10; # wait for x seconds to select the boot entry
 
   # add user's shell into /etc/shells
   environment.shells = with pkgs; [