fix(flake): detach nixos-uconsole nixpkgs from unstable to hit Cachix

nixos-uconsole's Cachix cache is built with nixpkgs-stable (25.11).
Following our unstable caused a full kernel rebuild every time.
By using nixos-uconsole's pinned nixpkgs, future builds will
download the pre-compiled kernel from the cache instead of
compiling it locally on the CM5.

flake.nix

@@ -18,7 +18,9 @@
     };
     nixos-uconsole = {
       url = "github:nixos-uconsole/nixos-uconsole";
-      inputs.nixpkgs.follows = "nixpkgs";
+      # Cache Cachix build avec nixpkgs stable (25.11).
+      # Ne PAS suivre notre unstable — sinon rebuild kernel à chaque fois.
+      # inputs.nixpkgs.follows = "nixpkgs";
     };
     nixos-raspberrypi = {
       url = "github:nvmd/nixos-raspberrypi/v1.20260517.0";