Scope filesystem permissions and drop sudo from the cache clear

[arhimede]

Four code blocks made data and log world-writable, and one told the reader to clear the config cache as root.

• chmod -R 777 on data and log is replaced with group ownership for the web-server user and 775. These are directories the web server writes into, and they hold the Twig and config caches, which are executable PHP — world-writable is a bad default to publish, and the pages offered no alternative and no scoping to local development. 777 is now mentioned once, in the FAQ, labelled as a throwaway-VM last resort.
• Added a note that the web-server user is apache on AlmaLinux and RHEL derivatives, since the page recommends AlmaLinux and the example says www-data.
• sudo php ./bin/clear-config-cache.php becomes composer clear-config-cache, with no sudo. Running it as root leaves the regenerated data/cache/config-cache.php owned by root and the application cannot rewrite it — which reproduces the exact permission errors the FAQ page exists to fix.