Fix npm executable path resolution in build script

frontend/build.gradle.kts

@@ -42,7 +42,7 @@ tasks.register("npmBuild") {
         commandLine(npmCmd, "run", "build")
       } else {
         val npmExecutable = file(nodeDir).listFiles()?.find { it.name.startsWith("npm") && it.isDirectory }?.let {
-          "${it.absolutePath}/npm"
+          "${it.absolutePath}/bin/npm/"
         } ?: "$nodeDir/node_modules/npm/bin/npm"
 
         commandLine(npmExecutable, "run", "build")