Second canonical loader. Reads canonical-persons.xlsx by header name and
upserts each register person via PersonService.upsertBySourceRef keyed on
the normalizer person_id. provisional is driven by the sheet's clean
value; Boolean.parseBoolean handles the capitalised Python "True"/"False".
ISO birth/death dates are reduced to the year the Person entity stores.
Refs #669
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>