The import corpus is uniform: every PDF is named <index>.pdf, so the
file column (the spreadsheet's datei value) is redundant. Remove file
from CanonicalDocument, RawRow, _FIELDS, to_canonical, and DOC_COLUMNS,
plus the now-moot index_file_mismatch review flag/CSV/stat and the
datei header mapping. date_end and the tree person_id are kept.
Refs #686
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
The unmatched list was just non-family correspondents (expected noise);
their count stays in summary.txt and they remain in canonical-persons.xlsx.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
