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/.gitignore

@@ -0,0 +1,25 @@
+# Dependencies
+node_modules
+.pnp
+.pnp.js
+
+# Build
+.next
+out
+build
+dist
+
+# Debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+
+# Local env
+.env*.local
+
+# Vercel
+.vercel
+
+# TypeScript
+*.tsbuildinfo
+next-env.d.ts