getCandidates, getMentorPool and bulkAssign matched MENTOR via roles[] only, so
a user with role=MENTOR but an empty roles[] array (legacy/seeded records, e.g.
Arnaud Blandin on prod) was excluded from the mentor picker and rejected by
bulk assign. Match MENTOR as primary role OR in roles[], mirroring userHasRole.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
