feat: allow unfree packages distro-wide

nixpkgs.config.allowUnfree in the system module (covers the live ISO
via useGlobalPkgs and every mkFlake machine) plus the two explicit
`import nixpkgs` sites (repo + lib.nix) so the standalone HM desktop
sees the same package set. Unblocks claude-code for the menu system's
ask-Claude module, vendor drivers, etc. Opt out with
`nixpkgs.config = lib.mkForce { allowUnfree = false; }`.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

modules/nixos/default.nix

@@ -14,6 +14,12 @@ in
   imports = [ ./options.nix ];
 
   config = {
+    # Unfree allowed distro-wide: pragmatic-desktop territory (claude-code
+    # for the menu's ask-Claude module, vendor drivers, …). The custom
+    # nixpkgs-config type can't carry a nested mkDefault; disagree with
+    # `nixpkgs.config = lib.mkForce { allowUnfree = false; }`.
+    nixpkgs.config.allowUnfree = true;
+
     # ── Wayland session: Hyprland ────────────────────────────────────
     # Installs the binary, registers the session, wires up
     # xdg-desktop-portal-hyprland. Configuration is Home Manager's job.