feat(uconsole): add rpi-cross-overlay module + Lix

- rpi-cross-overlay.nix: override pkgs.rpi with cross-compilation
  when buildPlatform != hostPlatform (0 QEMU)
- Lix nix daemon for uConsole (aarch64-linux)
- Remove broken inline overlay from flake.nix

modules/nixos/rpi-cross-overlay.nix

@@ -0,0 +1,40 @@
+# rpi-cross-overlay.nix
+#
+# Override pkgs.rpi to cross-compile when buildPlatform != hostPlatform.
+#
+# By default, nixos-raspberrypi's nixpkgs-rpi module creates pkgs.rpi via
+# mkRpiPkgs which imports nixpkgs with system="aarch64-linux" — a NATIVE
+# aarch64 build that requires QEMU on x86_64 builders.
+#
+# This module detects cross-compilation (buildPlatform != hostPlatform) and
+# re-imports pkgs.rpi using localSystem (builder) + crossSystem (target) so
+# that kernel, firmware, and rpi-optimized packages are genuinely cross-compiled
+# with zero QEMU emulation.
+#
+# Once nixos-raspberrypi upstream supports buildPlatform natively in mkRpiPkgs,
+# this module can be removed.
+
+{ config, lib, pkgs, nixos-raspberrypi, ... }:
+
+let
+  inherit (config.nixpkgs) buildPlatform hostPlatform;
+  isCross = buildPlatform.system != hostPlatform.system;
+in
+lib.mkIf isCross {
+  nixpkgs.overlays = [
+    (final: prev: {
+      rpi = import pkgs.path {
+        localSystem = { system = buildPlatform.system; };
+        crossSystem = { system = hostPlatform.system; };
+        overlays = with nixos-raspberrypi.overlays; [
+          bootloader
+          vendor-kernel
+          vendor-firmware
+          kernel-and-firmware
+          vendor-pkgs
+          pkgs
+        ];
+      };
+    })
+  ];
+}