Avoid renaming existing schema components

Serializers used only in a nested context have no complete form in the schema, so
prefixing them with "Brief" renamed an existing component to no purpose and dropped
the old name entirely. Exempt serializers declaring an explicit Meta.ref_name from
the prefix, and pin the three affected names.

This narrows the schema diff to the fields the bug actually affected: no components
are removed, and the nine which are added are purely additive.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>