Fail D1 sync when submitter metadata is missing

[bradvin]

Summary

• derive tool submitters from every tool PR, not only approved ones
• keep content validation submitter-agnostic for authors and PR validation
• fail D1 sync generation when a tool is missing PR-derived submitter metadata
• add regression coverage for missing submitter mappings during sync

Verification

• npm test
• npm run validate:content
• node ./scripts/generate-d1-sync-sql.mjs