feat(api): ApprovalRequestResponse 新增 metadata 欄位

讓前端/API 可見 incident_id，用於除錯和關聯追蹤

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api/src/models/approval.py

@@ -212,6 +212,8 @@ class ApprovalRequestResponse(BaseModel):
     fingerprint: str | None = None
     hit_count: int = 1
     last_seen_at: datetime | None = None
+    # Phase 6.5: Incident 關聯 (用於簽核後更新 Incident 狀態)
+    metadata: dict | None = None
 
     @classmethod
     def from_approval(cls, approval: ApprovalRequest) -> "ApprovalRequestResponse":
@@ -235,6 +237,8 @@ class ApprovalRequestResponse(BaseModel):
             fingerprint=approval.fingerprint,
             hit_count=approval.hit_count,
             last_seen_at=approval.last_seen_at,
+            # Phase 6.5
+            metadata=approval.metadata,
         )