feat: add rauta ontology evidence contract

[yairfalse]

Summary

• add a versioned Rauta ontology model for entity refs, diagnostic evidence, actions, time windows, and causal links
• attach structured ontology_evidence to diagnostics while preserving legacy human-readable evidence strings
• document the diagnostic ontology contract in README and CLAUDE

Validation

• cargo fmt --all -- --check
• cargo test --workspace
• cargo clippy --workspace --all-targets -- -D warnings
• teko verify --claim types --claim diagnostics --claim serialization --claim docs --json
• teko close --json