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/EstimateController.php

@@ -27,6 +27,15 @@ public function index(Request $request)
         ], __('message.fetched'));
     }
 
+    public function stats()
+    {
+        $stats = $this->estimateService->stats();
+
+        return ApiResponse::success([
+            'stats' => $stats,
+        ], __('message.fetched'));
+    }
+
     public function show($id)
     {
         $estimate = $this->estimateService->getEstimateDetail($id);