fix: include modifications missed by 528447c

Previous commit only picked up the new files (branding.nix, hardware-db.sh).
This adds the matching wires:

- core/system/default.nix: import branding.nix
- flake.nix: expose overlays.default = nomarchyOverlay for downstream flakes
- installer/disko-golden.nix: 1 GiB /boot, @snapshots subvolume, LUKS key
  via /dev/shm
- installer/install.sh: hardware auto-detect, hostname prompt, pinned
  nomarchy commit, shared pkgs in generated flake, flake.lock generation,
  post-install home-manager switch via nixos-enter

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

core/system/default.nix

@@ -4,6 +4,7 @@
   imports = [
     ./options.nix
     ./state.nix
+    ./branding.nix
     ./graphics.nix
     ./nix.nix
     ./scripts.nix