Ticket #76 PR #27 Review: pass_audit approved Drop artifacts and code_diffs database tables (left behind from ticket #58). Migration correctly uses drop_table with if_exists: true for safety. Includes necessary test updates - 6 spec files updated to remove references to removed models. Acceptance criteria all met: - Migration created ✓ - Schema updated (tables and foreign keys removed) ✓ - Migration runs safely ✓ - Tests updated to prevent failures ✓