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/LoanController.php

@@ -2,13 +2,13 @@
 
 namespace App\Http\Controllers\Api\V1;
 
+use App\Helpers\ApiResponse;
 use App\Http\Controllers\Controller;
 use App\Http\Requests\Loan\LoanCalculateInterestRequest;
 use App\Http\Requests\Loan\LoanIndexRequest;
 use App\Http\Requests\Loan\LoanSettleRequest;
 use App\Http\Requests\Loan\LoanStoreRequest;
 use App\Http\Requests\Loan\LoanUpdateRequest;
-use App\Helpers\ApiResponse;
 use App\Services\LoanService;
 use Illuminate\Http\JsonResponse;