fix(api): C-02+H-04 -- risk None crash and missing risk signals

C-02: Neo4j SUM() returns None (Python None) when no matching contract
rows exist. 'contract_rows' was always truthy (Cypher RETURN always
produces a row), so the 'if contract_rows else 0' guard never triggered.
f-string {total_crore:.1f} then crashed with TypeError.
Fix: added 'or 0' guard on the SUM value.

H-04: risk scoring only checked 4 signals and never queried
ElectoralBond, SanctionedEntity, or EnforcementAction nodes even
though all three types exist in the graph. High-risk patterns were
silently missed.
Fix: added 3 new risk factors: electoral_bond_donor (weight 0.20),
sanctions_exposure (weight 0.25), enforcement_action_subject (0.25).

api/routes/risk.py

@@ -54,7 +54,9 @@ def get_risk(entity_id: str, driver=Depends(get_db)):
         ).single()
 
         contract_count = contract_rows["contract_count"] if contract_rows else 0
-        total_crore    = contract_rows["total_crore"]    if contract_rows else 0
+        # C-02 FIX: SUM() returns None (Python None) when no rows match.
+        # None cannot be formatted with :.1f -- guard with "or 0"
+        total_crore = (contract_rows["total_crore"] if contract_rows else 0) or 0
 
         if contract_count and contract_count > 0:
             raw = min(contract_count * 10, 35)