fix(api): BUG-12 -- SearchResult model missing risk_level field

The frontend ResultCard component renders:
class='risk-badge risk-badge--${entity.risk_level || "LOW"}'

risk_level was never in the SearchResult Pydantic model so it
was never included in API responses. Every search result risk
badge rendered as LOW regardless of actual risk. Added
risk_level: Optional[str] = None to SearchResult.

api/models.py

@@ -21,6 +21,10 @@ class SearchResult(BaseModel):
     state: Optional[str] = None
     party: Optional[str] = None
     risk_score: Optional[int] = None
+    # BUG-12 FIX: risk_level was missing -- frontend Components.ResultCard renders
+    # class="risk-badge risk-badge--${entity.risk_level}" so without this field
+    # every badge was always risk-badge--undefined which rendered as LOW visually.
+    risk_level: Optional[str] = None
     sources: List[SourceDocument] = []