Citations

@dataclass
class Citation:
    citation_id: str
    source_type: str           # "guideline" | "ontology" | "knowledge_base" | "payer_rule"
    source_name: str
    source_url: Optional[str]
    evidence_level: str
    relevance_score: float
    retrieved_at: datetime
    content_snippet: str       # max 200 chars