fix(#10): Add Docker HEALTHCHECK on /health endpoint and document healthy/unhealthy criteria

Dockerfile.test

@@ -7,4 +7,6 @@ RUN npm ci
 
 COPY backend/ ./
 
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 CMD curl -f http://localhost:3000/health || exit 1
+
 CMD ["npm", "test"]

docs/healthcheck.md

@@ -0,0 +1,35 @@
+# Healthcheck
+
+## Endpoint
+
+The application exposes a `/health` endpoint at the root level which returns a JSON response indicating the health status of the application.
+
+### Example Response
+
+```json
+{
+  "status": "ok"
+}
+```
+
+## Docker HEALTHCHECK
+
+The Docker image includes a `HEALTHCHECK` instruction that verifies the application's health by making an HTTP request to the `/health` endpoint.
+
+### Healthcheck Configuration
+
+- **Interval**: 30 seconds
+- **Timeout**: 10 seconds
+- **Start Period**: 5 seconds
+- **Retries**: 3 attempts
+
+### Healthy Status
+
+The container is considered healthy if the `/health` endpoint returns a successful HTTP response (status code 2xx).
+
+### Unhealthy Status
+
+The container is considered unhealthy if:
+
+1. The `/health` endpoint is unreachable.
+2. The `/health` endpoint returns an error status code (4xx or 5xx).