Add Drupal headless stack with Next.js frontend

- Add Next.js frontend service (nextjs) with Dockerfile and source
- Update docker-compose.yml: image names, Drupal 11.3.3, nextjs service
- Add docker-compose.override.yml.disabled for dev hot-reload
- Add install-headless-modules.sh for OAuth/JSON:API module setup
- Add README.md with full setup and configuration guide
- Update nginx/Dockerfile and nginx.conf.template for cms. subdomain
- Update drupal/Dockerfile PHP-FPM build args
- Gitignore **/.vscode/ to prevent IDE workspace files from being tracked

drupal/nextjs/public/assets/icons/youtube.svg

@@ -0,0 +1,20 @@
+<?xml version="1.0" standalone="no"?>
+<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
+ "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
+<svg version="1.0" xmlns="http://www.w3.org/2000/svg"
+ width="397.000000pt" height="278.000000pt" viewBox="0 0 397.000000 278.000000"
+ preserveAspectRatio="xMidYMid meet">
+<metadata>
+Created by potrace 1.16, written by Peter Selinger 2001-2019
+</metadata>
+<g transform="translate(0.000000,278.000000) scale(0.100000,-0.100000)"
+fill="#475569" stroke="none">
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+</g>
+</svg>