- Adds schemas/provenance.json defining provenance object schema
- Updates harvester.py write_knowledge() to attach provenance to every fact
- Adds extract_provider() helper to infer provider from API base URL
- Updates SCHEMA.md documenting provenance field and object
- Provenance fields: source_session, source_model, source_provider,
timestamp (harvested_at), extraction_method, confidence, verified
- Does NOT retroactively modify existing facts in index.json
Closes#197