Run container as unprivileged www-data user and simplify entrypoint

- Remove root-only FPM user configuration from entrypoint.sh (moved to Dockerfile build time)
- Remove Redis session configuration from entrypoint.sh (handled by Symfony services)
- Remove cache directory permission adjustments (unnecessary with proper ownership)
- Set file ownership to www-data:www-data at build time using COPY --chown
- Create required directories and set ownership in single RUN layer
- Switch to www-data USER before CMD
- Remove PHP_FPM_USER, PHP_FPM_GROUP, SESSION_LIFETIME environment variables
- Add docker/ directory to .dockerignore

Dockerfile

@@ -1,31 +1,38 @@
 FROM chill/base-image:8.4-edge
 
-# copy directories
+# copy directories with ownership for the unprivileged runtime user
+COPY --chown=www-data:www-data ./bin    /var/www/app/bin/.
+COPY --chown=www-data:www-data ./composer.* /var/www/app/
+COPY --chown=www-data:www-data ./config    /var/www/app/config/.
+COPY --chown=www-data:www-data ./migrations /var/www/app/migrations/.
+COPY --chown=www-data:www-data ./public    /var/www/app/public/.
+COPY --chown=www-data:www-data ./src    /var/www/app/src/.
+COPY --chown=www-data:www-data ./templates /var/www/app/templates/.
+COPY --chown=www-data:www-data ./translations /var/www/app/translations/.
+COPY --chown=www-data:www-data ./vendor /var/www/app/vendor/.
 
-COPY ./bin    /var/www/app/bin/.
-COPY ./composer.* /var/www/app/
-COPY ./config    /var/www/app/config/.
-COPY ./migrations /var/www/app/migrations/.
-COPY ./public    /var/www/app/public/.
-COPY ./src    /var/www/app/src/.
-COPY ./templates /var/www/app/templates/.
-COPY ./translations /var/www/app/translations/.
-COPY ./vendor /var/www/app/vendor/.
-
-COPY ./.env /var/www/app/.env
+COPY --chown=www-data:www-data ./.env /var/www/app/.env
 
 # import the manifest.json file
-COPY ./public/build/manifest.json /var/www/app/public/build/manifest.json
+COPY --chown=www-data:www-data ./public/build/manifest.json /var/www/app/public/build/manifest.json
 
-ADD ./entrypoint.sh /.
+COPY ./entrypoint.sh /entrypoint.sh
 
-RUN chmod +x /entrypoint.sh
+# - mark entrypoint executable
+# - declare the FPM pool user/group at build time (was previously written by entrypoint.sh as root)
+# - prepare writable Symfony var/ and COMPOSER_HOME directories for the unprivileged runtime user
+RUN chmod +x /entrypoint.sh \
+    && printf '[www]\nuser=www-data\ngroup=www-data\n' > /usr/local/etc/php-fpm.d/zz-user.conf \
+    && mkdir -p /var/www/app/var/cache /var/www/app/var/log /var/www/app/.composer \
+    && chown -R www-data:www-data /var/www/app/var /var/www/app/.composer \
+    && chown www-data:www-data /var/www/app
+# php-fpm listens on 9000 by default (unprivileged port)
+EXPOSE 9000
+
+USER www-data
 
 ENTRYPOINT ["/entrypoint.sh"]
 
-ENV PHP_FPM_USER=www-data \
-    PHP_FPM_GROUP=www-data \
-    COMPOSER_HOME=/var/www/app/.composer \
-    SESSION_LIFETIME=10800
+ENV COMPOSER_HOME=/var/www/app/.composer
 
 CMD [ "php-fpm" ]