[C2] Clean uploaded temp files

[ywarnier]

Files are now uploaded asynchronously, but this means if many files are uploaded and some are then removed from the list before submitting the form, the deleted files will remain in a temporary folder until deletion by a later process.
To avoid this, a process of cleaning (possibly together with cache) should be offered through the admin interface and as a cron task.

Steps to implement:

• locate the directory holding the files temporarily until they are moved to their final destination (let's say we call that $tempUploadFolder)
• on /main/admin/archive_cleanup.php, make sure when you click "Proceed with cleanup", the $tempUploadFolder is emptied of all files
• in php bin/console cache:clear, add an option to clear the temporary upload folder (--upload-folder) or create a new command cache:clear-uploads, so that it can easily be "chroned" later on

[christianbeeznest]

It is implemented with this PR #6601

• Introduce TempUploadHelper to clean uploaded temp files under var/cache,
  safely excluding Symfony cache subtrees.
• Add admin page (/admin/cleanup-temp-uploads) with stats, CSRF, dry-run,
  and "older-than (minutes)" TTL; Tailwind-styled.
• On cleanup: remove public/build main*.js and refresh assets via ScriptHandler::dumpCssFiles().
• Provide CLI command cache:clear-uploads with --older-than, --dry-run, and --dir for cron.

Thanks for confirmation.

[ywarnier]

Good job 👍