Behaviour tests for export (json/csv/errors), duplicate detection and
merging, image metadata storage and lookup, missing-file cleanup,
statistics, bulk operations, orphan pruning, consistency checks,
subfolder listing, tag queries and management edge cases, legacy tag
column parsing, config-driven path resolution, model housekeeping and
the TEXT -> INTEGER prompt_id migration. database/operations.py and
database/models.py are both above 85% statement+branch coverage.