Add entrypoint script to create .env from Docker environment variables

Dockerfile

@@ -23,6 +23,10 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && curl -o /usr/local/bin/wp https://raw.githubusercontent.com/wp-cli/builds/gh-pages/phar/wp-cli.phar \
     && chmod +x /usr/local/bin/wp
 
+# Copy entrypoint script
+COPY docker-entrypoint.sh /usr/local/bin/
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
 # Copy application
 USER www-data
 WORKDIR /var/www/html
@@ -36,3 +40,6 @@ HEALTHCHECK --interval=30s --timeout=10s --start-period=60s --retries=3 \
     CMD curl -fsS http://localhost/ -o /dev/null || exit 1
 
 EXPOSE 80
+
+ENTRYPOINT ["docker-entrypoint.sh"]
+CMD ["/init"]