Two bugs preventing screenshot display in report UI:
1. Plugin's ValidationRecord constructor did NOT include
screenshot_paths (plural, JSON array). The column stayed NULL
even though paths were stored in raw_response. Records created
by the plugin now include screenshot_paths=webp_paths|jpeg_paths.
2. Backward compat for existing records: _record_to_dict now
falls back to extracting screenshot_paths from raw_response JSON
when the DB column is empty.
Also fixes: broken import statement in validation_service.py
(missing closing paren + missing imports from earlier edit).