fix: remplacer import atomicptr par crab.nix local

Corrige le warning d'évaluation "'system' has been renamed to
stdenv.hostPlatform.system" causé par `system = system` dans la
dérivation crab upstream.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages.nix

@@ -13,8 +13,7 @@ let
   };
 in
 let
-  atomicptr = import (fetchTarball
-    "https://github.com/atomicptr/nix/archive/refs/heads/master.tar.gz") { };
+  crab = pkgs.callPackage ./pkgs/crab.nix { };
   rtk = pkgs.callPackage ./pkgs/rtk.nix { };
 in {
   nixpkgs.overlays = [ pythonOverlay ];
@@ -52,7 +51,7 @@ in {
     hey
     ngrok
     openssl
-    atomicptr.crab
+    crab
 
     pulseaudioFull
     pavucontrol