feat: Phase 8 SaaS 확장 - 구독관리/결제내역 API 추가

- 사용량 조회 API (GET /subscriptions/usage)
- 데이터 내보내기 API (POST/GET /subscriptions/export)
- 결제 명세서 API (GET /payments/{id}/statement)
- DataExport 모델 및 마이그레이션 추가

app/Http/Controllers/Api/V1/SubscriptionController.php

@@ -3,6 +3,7 @@
 namespace App\Http\Controllers\Api\V1;
 
 use App\Http\Controllers\Controller;
+use App\Http\Requests\V1\Subscription\ExportStoreRequest;
 use App\Http\Requests\V1\Subscription\SubscriptionCancelRequest;
 use App\Http\Requests\V1\Subscription\SubscriptionIndexRequest;
 use App\Http\Requests\V1\Subscription\SubscriptionStoreRequest;
@@ -95,4 +96,34 @@ public function resume(int $id): JsonResponse
 
         return ApiResponse::handle('message.subscription.resumed', $result);
     }
+
+    /**
+     * 사용량 조회
+     */
+    public function usage(): JsonResponse
+    {
+        $result = $this->subscriptionService->usage();
+
+        return ApiResponse::handle('message.fetched', $result);
+    }
+
+    /**
+     * 내보내기 요청
+     */
+    public function export(ExportStoreRequest $request): JsonResponse
+    {
+        $result = $this->subscriptionService->createExport($request->validated());
+
+        return ApiResponse::handle('message.export.requested', $result, 201);
+    }
+
+    /**
+     * 내보내기 상태 조회
+     */
+    public function exportStatus(int $id): JsonResponse
+    {
+        $result = $this->subscriptionService->getExport($id);
+
+        return ApiResponse::handle('message.fetched', $result);
+    }
 }