Fix harness crash: load standalone config to skip webpack in production

The standalone next package is trimmed and doesn't include webpack.
The custom server.js was using next() which triggers config loading
that requires webpack. Fix by extracting the standalone config at
build time and setting __NEXT_PRIVATE_STANDALONE_CONFIG before
requiring next, matching what the generated standalone server does.

apps/harness/server.js

@@ -1,13 +1,26 @@
 const { createServer } = require("http");
+const path = require("path");
 const { parse } = require("url");
-const next = require("next");
-const { attachPtyWebSocket } = require("./pty-server");
 
 const dev = process.env.NODE_ENV !== "production";
 const hostname = process.env.HOSTNAME || "0.0.0.0";
 const port = parseInt(process.env.PORT || "3100", 10);
 
-const app = next({ dev, hostname, port });
+// In production, load the standalone config to avoid webpack dependency
+if (!dev) {
+  try {
+    const configPath = path.join(__dirname, "next-config.json");
+    const nextConfig = JSON.parse(require("fs").readFileSync(configPath, "utf8"));
+    process.env.__NEXT_PRIVATE_STANDALONE_CONFIG = JSON.stringify(nextConfig);
+  } catch {
+    // Config not found (local dev) — next() will load config normally
+  }
+}
+
+const next = require("next");
+const { attachPtyWebSocket } = require("./pty-server");
+
+const app = next({ dev, hostname, port, dir: __dirname });
 const handle = app.getRequestHandler();
 
 app.prepare().then(() => {