RebacManager.get_queryset() hardcoded `RebacQuerySet(...)`, which defeated
`RebacManager.from_queryset(CustomQuerySet)` — the dynamically-assigned
`_queryset_class` was ignored and downstream subclass methods silently fell
back to the base class.

Bumps version to 0.1.5.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>