Install the epub skill's documented test dependencies (EbookLib and
beautifulsoup4) on the runner just before the shell-test step, and move
epub/scripts/test_epub_skill.sh from the manual registry into the run
registry. EbookLib is AGPL-licensed, so the install step is named and
scoped as test-only and does not touch requirements-dev.txt.
Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>