feat: initial health-app with Express API and GitOps CI/CD

Node.js Express app with /health, /ready, / endpoints.
Multi-stage Dockerfile, GitHub Actions pipeline for GHCR push
and gitops-infra manifest auto-update.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/server.js

@@ -0,0 +1,52 @@
+"use strict";
+
+const express = require("express");
+
+const app = express();
+const PORT = parseInt(process.env.PORT, 10) || 3000;
+const startTime = Date.now();
+
+app.disable("x-powered-by");
+
+app.get("/", (_req, res) => {
+  res.json({
+    service: "health-app",
+    version: process.env.APP_VERSION || "1.0.0",
+    environment: process.env.NODE_ENV || "development",
+  });
+});
+
+app.get("/health", (_req, res) => {
+  res.json({
+    status: "healthy",
+    uptime: Math.floor((Date.now() - startTime) / 1000),
+    timestamp: new Date().toISOString(),
+    memoryUsage: process.memoryUsage().rss,
+  });
+});
+
+app.get("/ready", (_req, res) => {
+  res.json({ ready: true });
+});
+
+app.use((_req, res) => {
+  res.status(404).json({ error: "Not Found" });
+});
+
+app.use((err, _req, res, _next) => {
+  console.error("Unhandled error:", err.message);
+  res.status(500).json({ error: "Internal Server Error" });
+});
+
+const server = app.listen(PORT, "0.0.0.0", () => {
+  console.log(`health-app listening on port ${PORT}`);
+});
+
+function shutdown(signal) {
+  console.log(`${signal} received, shutting down gracefully`);
+  server.close(() => process.exit(0));
+  setTimeout(() => process.exit(1), 10000);
+}
+
+process.on("SIGTERM", () => shutdown("SIGTERM"));
+process.on("SIGINT", () => shutdown("SIGINT"));