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/SalaryController.php

@@ -123,4 +123,4 @@ public function statistics(Request $request)
 
         return ApiResponse::success($stats, __('message.fetched'));
     }
-}
+}