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>

flake.nix

@@ -38,13 +38,14 @@
     system = "x86_64-linux";
     lib = nixpkgs.lib;
 
-    # Overlays
-    overlays = [
-      (final: prev: {
-        makima-bin = prev.makima;
-        nomarchy-system-scripts = final.callPackage ./core/system/scripts-derivation.nix { };
-      })
-    ];
+    # Overlays — the function form lives here so both Nomarchy itself and
+    # any downstream flake (see `overlays.default` in the outputs) can layer
+    # the same Nomarchy packages onto their nixpkgs.
+    nomarchyOverlay = final: prev: {
+      makima-bin = prev.makima;
+      nomarchy-system-scripts = final.callPackage ./core/system/scripts-derivation.nix { };
+    };
+    overlays = [ nomarchyOverlay ];
 
     pkgs = import nixpkgs {
       inherit system overlays;
@@ -90,6 +91,12 @@
     # Expose inputs for downstream use
     inherit inputs;
 
+    # Downstream flakes consume this to layer Nomarchy's packages onto their
+    # own nixpkgs. Used by the installer-generated flake so both the
+    # nixosSystem and the standalone homeManagerConfiguration share one
+    # `pkgs` with the overlay applied.
+    overlays.default = nomarchyOverlay;
+
     nixosModules = {
       system = import ./core;
       home = import ./features;