feat: Add DevContainer and Codespaces support for docker-master

[Ramjivan]

🎯 What this does:

1. Zero manual setup: A contributor can clone the repo on this branch, click "Reopen in Container", and the environment will build and seed automatically using the php (php-fpm) container.
2. Codespaces Ready: Configured so anyone can spin up a free GitHub Codespace directly from this branch and have a working Rox environment in their browser.
3. Xdebug added: xdebug is installed in the bewelcome_php_dev stage and configured via bewelcome.xdebug.ini to allow easy local debugging out of the box (defaulted to off so it does not degrade performance during normal use).
4. Ports: Standard ports (80 for Web/Nginx, 1080 for Mailcatcher) are auto-forwarded and labelled for a cleaner experience.

(Note: The previous PR #484 was against develop. This correctly targets feature/docker-master as requested by Peter.)

[Ramjivan]

Closing as duplicate of #484. I'll update #484 to target the correct branch instead.