Add nixpkgs-uconsole pinned to commit that base image used

The base image (nixos-uconsole v1.1.0) was built with nixpkgs
commit 54170c54449ea4d6725efd30d719c5e505f1c10e (2026-04-10),
NOT the flake.lock pin (89dbf01df7 from Dec 2025). By pinning to
the exact commit the image used, the kernel derivation hash should
match what's already in the store.

flake.nix

@@ -16,8 +16,12 @@
       url = "git+https://git.lix.systems/lix-project/lix?ref=main";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    nixpkgs-uconsole = {
+      url = "github:nixos/nixpkgs/54170c54449ea4d6725efd30d719c5e505f1c10e";
+    };
     nixos-uconsole = {
       url = "github:nixos-uconsole/nixos-uconsole/v1.1.0";
+      inputs.nixpkgs.follows = "nixpkgs-uconsole";
     };
     nixos-raspberrypi = {
       url = "github:nvmd/nixos-raspberrypi/v1.20260317.0";