Return the hosted_default revision/audit history for one scope_id, newest first. Mirrors the get_profile_layer_revisions MCP tool — a non-hosted_default scope_id always returns [].

Registered BEFORE get_profile_layer_route below: both are GET routes with the same 2-segment shape (/profile-layers/<a>/<b>), and Starlette matches routes in registration order — the literal-suffixed .../revisions route must be tried first or the fully-wildcarded {scope_type}/{scope_id} route below would always shadow it (e.g. GET /profile-layers/global/revisions would resolve as scope_type="global", scope_id="revisions" instead).