feat: Replace dynamic ports with shared development proxy

[vitormattos]

Replaces the dynamic nginx port selector with a shared nginx-proxy based development proxy.

This change provides predictable *.localhost URLs, automatic local HTTPS certificates, support for multiple concurrent checkouts, proxy reuse across environments, and clearer handling of port 80/443 conflicts.

The developer workflow remains:

docker compose up

Follow an example of starting services:

nextcloud-1          | 📅 Running cron for the first time ...
nextcloud-1          | Starting PHP-FPM...
nextcloud-1          | [21-Aug-2026 18:37:21] NOTICE: fpm is running, pid 1
nextcloud-1          | [21-Aug-2026 18:37:21] NOTICE: ready to handle connections
nextcloud-1          | 
nextcloud-1          | ┌─ 💙 Environment ready ───────────────────────────
nextcloud-1          | │
nextcloud-1          | │ Nextcloud       https://testenv.localhost
nextcloud-1          | │ Mailpit         https://testenv-mailpit.localhost
nextcloud-1          | │
nextcloud-1          | │ Nextcloud branch master
nextcloud-1          | │ Admin user       admin
nextcloud-1          | │ Admin password   admin
nextcloud-1          | │
nextcloud-1          | │ 🔐 HTTPS uses the LibreCode local development CA.
nextcloud-1          | │    Trust it once if your browser shows a warning.
nextcloud-1          | │
nextcloud-1          | └──────────────────────────────────────────────────
proxy-coordinator-1  | ✅ Existing LibreCode development proxy reused. Coordinator exiting normally.
proxy-coordinator-1 exited with code 0

Now, when access localhost, will display the follow page: