feat: Product API에 FormRequest 및 i18n 적용

- ProductStoreRequest, ProductUpdateRequest 생성
- ProductController에 FormRequest 적용
- 하드코딩된 메시지를 i18n 키로 변경
- lang/ko/message.php에 product 관련 메시지 키 추가
- SAM API Development Rules 준수

Phase 3-1: ProductApi.php Swagger 점검 완료

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

@@ -4,6 +4,8 @@
 
 use App\Helpers\ApiResponse;
 use App\Http\Controllers\Controller;
+use App\Http\Requests\Product\ProductStoreRequest;
+use App\Http\Requests\Product\ProductUpdateRequest;
 use App\Services\ProductService;
 use Illuminate\Http\Request;
 
@@ -15,7 +17,7 @@ public function getCategory(Request $request)
     {
         return ApiResponse::handle(function () use ($request) {
             return $this->service->getCategory($request);
-        }, '제품 카테고리 조회');
+        }, __('message.product.category_fetched'));
     }
 
     // GET /products
@@ -23,15 +25,15 @@ public function index(Request $request)
     {
         return ApiResponse::handle(function () use ($request) {
             return $this->service->index($request->all());
-        }, '제품 목록');
+        }, __('message.product.fetched'));
     }
 
     // POST /products
-    public function store(Request $request)
+    public function store(ProductStoreRequest $request)
     {
         return ApiResponse::handle(function () use ($request) {
-            return $this->service->store($request->all());
-        }, '제품 생성');
+            return $this->service->store($request->validated());
+        }, __('message.product.created'));
     }
 
     // GET /products/{id}
@@ -39,15 +41,15 @@ public function show(int $id)
     {
         return ApiResponse::handle(function () use ($id) {
             return $this->service->show($id);
-        }, '제품 단건');
+        }, __('message.product.fetched'));
     }
 
     // PATCH /products/{id}
-    public function update(int $id, Request $request)
+    public function update(int $id, ProductUpdateRequest $request)
     {
         return ApiResponse::handle(function () use ($id, $request) {
-            return $this->service->update($id, $request->all());
-        }, '제품 수정');
+            return $this->service->update($id, $request->validated());
+        }, __('message.product.updated'));
     }
 
     // DELETE /products/{id}
@@ -57,7 +59,7 @@ public function destroy(int $id)
             $this->service->destroy($id);
 
             return 'success';
-        }, '제품 삭제');
+        }, __('message.product.deleted'));
     }
 
     // GET /products/search
@@ -65,7 +67,7 @@ public function search(Request $request)
     {
         return ApiResponse::handle(function () use ($request) {
             return $this->service->search($request->all());
-        }, '제품 검색');
+        }, __('message.product.searched'));
     }
 
     // POST /products/{id}/toggle
@@ -73,6 +75,6 @@ public function toggle(int $id)
     {
         return ApiResponse::handle(function () use ($id) {
             return $this->service->toggle($id);
-        }, '제품 활성 토글');
+        }, __('message.product.toggled'));
     }
 }