Bind the example app to localhost by default when debug mode is enabled

Hi, thanks for maintaining this example project. I noticed a small safety improvement that may help prevent accidental exposure when people copy the example configuration into a development or staging environment.

The current .env.example development defaults enable FLASK_DEBUG=true and publish the web service with DOCKER_WEB_PORT_FORWARD=8000. In Docker Compose, that publishes the port on all host interfaces. If someone runs the sample on a laptop, VM, cloud dev box, or shared network, the Werkzeug debugger / console can become reachable from outside the local machine.

This looks intentional for local development convenience, not a framework vulnerability. Still, since this repository is often used as a starting template, it may be safer to bind the default forwarded port to loopback only:

export DOCKER_WEB_PORT_FORWARD=127.0.0.1:8000

That preserves the normal local browser workflow while reducing the chance that the debug console is exposed on a LAN or public interface by accident.

Suggested changes:

• Bind the default development port to 127.0.0.1:8000.
• Add a short warning near FLASK_DEBUG=true and the port forwarding setting that debug mode and Werkzeug's interactive debugger should not be exposed to untrusted networks.
• Optionally mention in the README that developers who need another device to access the app can explicitly change DOCKER_WEB_PORT_FORWARD, but should not do so with debug mode enabled on untrusted networks.

I can open a small PR for this if you agree with the direction.

Start with .env.example and inspect how DOCKER_WEB_PORT_FORWARD is used by Docker Compose, then review the README for the development setup. Update the default binding and add the warning about FLASK_DEBUG and Werkzeug's debugger; done means local access still works while the default port binds only to localhost and the documentation explains the explicit override.