fix(api): bulk-approve BlastRadius 屬性存取錯誤

bug: approval.blast_radius.get("data_impact") → AttributeError
fix: 改為 approval.blast_radius.data_impact (Pydantic model 屬性)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/api/v1/approvals.py

@@ -566,7 +566,7 @@ async def bulk_approve(
                 continue
 
             # 🔴 安全限制: DESTRUCTIVE 禁止批次核准
-            if approval.blast_radius and approval.blast_radius.get("data_impact") == "DESTRUCTIVE":
+            if approval.blast_radius and approval.blast_radius.data_impact == "DESTRUCTIVE":
                 results.append(BulkApproveResult(
                     approval_id=approval_id_str,
                     success=False,