Replace DefaultCollectionRedirect with a CollectionDirectory that lists the
project's visible collections, or redirects into the sole one when there is
exactly one (preserving the S1 C3.7/C3.8 single-collection UX). The
create-first-collection empty state is S4.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>