revert: keep rkey for leaflet URLs, slug paths are unreliable
checked turso: only 20 leaflet docs have custom slugs, and most of
those slug URLs actually 404 on leaflet.pub (piffey, meri) while the
rkey URLs work fine. the ann.leaflet.pub case where rkey 404s and slug
works is the exception, not the rule. reverting to rkey-based URLs.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>