fix: pre-fetch swagger-ui assets for Nix sandbox build

default.nix

@@ -1,4 +1,10 @@
 { pkgs ? import <nixpkgs> { } }:
+let
+  swaggerUi = pkgs.fetchurl {
+    url = "https://github.com/swagger-api/swagger-ui/archive/refs/tags/v5.17.14.zip";
+    hash = "sha256-SBJE0IEgl7Efuu73n3HZQrFxYX+cn5UU5jrL4T5xzNw=";
+  };
+in
 pkgs.rustPlatform.buildRustPackage {
   pname = "imphnen-backend";
   version = (pkgs.lib.importTOML ./imphnen-backend/Cargo.toml).package.version;
@@ -12,5 +18,8 @@ pkgs.rustPlatform.buildRustPackage {
   ];
   nativeBuildInputs = [ pkgs.pkg-config ];
   buildInputs = [ pkgs.openssl ];
+  preBuild = ''
+    export SWAGGER_UI_DOWNLOAD_URL="file://${swaggerUi}"
+  '';
   doCheck = false;
 }