Move DocumentTitleFormatter from importing into the document package and
introduce DocumentTitleFactory there as the single source of truth for the
{index} – {dateLabel} – {location} formula. DocumentImporter now consumes the
factory instead of owning the composition; the document package owns the rule,
importing depends on it (not the reverse). No behavioral change — importer
title assertions and the #666 fixture parity test stay green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>