Build the frontend with nix and add to container

nix/containers.nix

@@ -25,6 +25,23 @@ staticFiles = pkgs.buildEnv {
   extraOutputsToInstall = [ "/html" ];
 };
 
+frontendNpm = pkgs.buildNpmPackage rec {
+  name = "frontend";
+  src = ../frontend;
+  npmDepsHash = "sha256-Oz7pdTMJVgGj5rzjIMvDjaOV7JU+hYLHoSSb+OcJARk=";
+  npmPackFlags = [ "--ignore-scripts" ];
+  installPhase = ''
+    mkdir -p $out/_next
+    cp -r .next/* $out/_next
+    rm -rf $out/_next/cache
+  '';
+};
+
+frontend = pkgs.buildEnv {
+  name = "frontend";
+  paths = [ frontendNpm ];
+};
+
 in rec {
 
   # Builds a docker container for the cabal executable given as input. First we
@@ -52,8 +69,9 @@ in rec {
       Entrypoint = lib.singleton (lib.getExe inputs.self.packages.wst-poc-cli);
     };
     layers = [
+      # npm-created data for frontend
       (inputs.n2c.packages.nix2container.buildLayer {
-        copyToRoot = [staticFiles];
+        copyToRoot = [frontend];
       })
     ];
   };