fix(API): Controller 타입 및 코드 정리

- FcmController, EstimateController, ItemsController 개선
- LoanController, PositionController 수정
- ReceivablesController, SalaryController 수정
- StructureReviewController 수정

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

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

@@ -100,4 +100,4 @@ public function updateMemos(Request $request): JsonResponse
             return ['updated_count' => $updatedCount];
         }, __('message.updated'));
     }
-}
+}