Replace command-not-found with nix-index

configuration.nix

@@ -156,6 +156,13 @@ with pkgs;
   # Enable fish package completion
   programs.fish.enable = true;
 
+  # Enable nix-index
+  programs.command-not-found.enable = false;
+  programs.nix-index = {
+    enable = true;
+    enableFishIntegration = true;
+  };
+
   # Import other configuration modules
   imports = [
     ./modules/hardware-configuration.nix