feat: [finance] vendors 및 supplier-settings API 추가

- GET /api/v1/vendors: 거래처 간단 목록 (id, name) 반환
- GET /api/v1/tax-invoices/supplier-settings: 공급자 설정 조회
- PUT /api/v1/tax-invoices/supplier-settings: 공급자 설정 저장

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

@@ -20,6 +20,16 @@ public function index(Request $request)
         }, __('message.client.fetched'));
     }
 
+    /**
+     * 거래처 간단 목록 (id, name만 반환) - vendors 엔드포인트용
+     */
+    public function vendors(Request $request)
+    {
+        return ApiResponse::handle(function () use ($request) {
+            return $this->service->vendors($request->all());
+        }, __('message.client.fetched'));
+    }
+
     public function show(int $id)
     {
         return ApiResponse::handle(function () use ($id) {