- Created cleanup-invalid-tenders.mjs script to validate tender URLs
- Detects removed tenders via redirect to /syserror/notfound
- Marks invalid tenders as closed in database
- Initial run found 277/626 tenders (~44%) already removed from sources
- Contracts Finder has highest removal rate (tenders removed before deadline)
- Add comprehensive documentation in TENDER_CLEANUP_SUMMARY.md
