Removed kbcstorage from all dependency groups (optional + dev) so urllib3
is no longer pinned to <2.0. Legacy Keboola client is available via
manual install: pip install kbcstorage
kbcstorage pins urllib3<2.0.0 which blocks Dependabot security patches.
Moved to [project.optional-dependencies] keboola-legacy since the primary
extraction path uses the DuckDB Keboola extension, not kbcstorage.
Legacy fallback uses lazy import — app works without it installed.