feat: add health check script and update Dockerfile for health check integration

healthcheck.js

@@ -0,0 +1,39 @@
+#!/usr/bin/env node
+"use strict";
+
+const http = require("node:http");
+
+const port = Number.parseInt(process.env.PORT || "3000", 10);
+const path = process.env.HEALTHCHECK_PATH || "/api/templates";
+const timeoutMs = Number.parseInt(process.env.HEALTHCHECK_TIMEOUT_MS || "3000", 10);
+
+const req = http.request(
+  {
+    host: "127.0.0.1",
+    port,
+    path,
+    method: "GET",
+    timeout: timeoutMs
+  },
+  (res) => {
+    // Drain the response so the socket can close cleanly.
+    res.resume();
+
+    if (res.statusCode && res.statusCode >= 200 && res.statusCode < 400) {
+      process.exit(0);
+      return;
+    }
+
+    process.exit(1);
+  }
+);
+
+req.on("timeout", () => {
+  req.destroy(new Error("healthcheck timeout"));
+});
+
+req.on("error", () => {
+  process.exit(1);
+});
+
+req.end();