hello-node: minimal HTTP server for the host-app POC

package.json

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+{
+  "name": "hello-node",
+  "version": "1.0.0",
+  "scripts": { "start": "node server.js" }
+}

server.js

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+const http = require("http");
+const port = process.env.PORT || 3000;
+http.createServer((req, res) => {
+  res.writeHead(200, { "Content-Type": "text/plain" });
+  res.end(`hello from the yourai app platform\napp: hello-node\ngreeting: ${process.env.GREETING || "(unset)"}\n`);
+}).listen(port, () => console.log(`listening on ${port}`));