feat: Docker Hub image, cloaktest CLI, and example UX improvements

Add cloakhq/cloakbrowser Docker Hub image with Node.js, JS wrapper,
Xvfb headed mode, and cloaktest shortcut. Add launch feedback and IP
display to all examples. Update README Docker section for Docker Hub.

bin/docker-entrypoint.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+# Start Xvfb for headed mode (Turnstile, CAPTCHAs), then run user command
+Xvfb :99 -screen 0 1920x1080x24 -nolisten tcp &
+sleep 1
+exec "$@"