feat: Testing with external peers

[r-zig]

Description

This PR updates the js-libp2p-example-webrtc-private-to-private example to support and document testing peer-to-peer connectivity in realistic network conditions, such as when peers are:

Running on separate machines
Behind NATs or VPNs
Without public IPs
Key changes include:

Binding the development server to all interfaces (0.0.0.0), so the example is reachable from external machines.
Documentation for exposing port 5173, including guidance for environments like AWS EC2.
Recommendation to use a static public IP for the signaling server host to avoid connectivity issues.
Connection type indicator: The UI now displays whether a peer connection is established Directly or via a Relay.
Fixes #226.

Notes & open questions

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if necessary (this includes comments as well)
• I have added tests that prove my fix is effective or that my feature works