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/Services/ClientService.php

@@ -113,6 +113,22 @@ public function index(array $params)
         return $paginator;
     }
 
+    /**
+     * 거래처 간단 목록 (id, name만 반환) - vendors 엔드포인트용
+     */
+    public function vendors(array $params): array
+    {
+        $tenantId = $this->tenantId();
+        $perPage = (int) ($params['per_page'] ?? 9999);
+
+        return Client::where('tenant_id', $tenantId)
+            ->where('is_active', true)
+            ->orderBy('name')
+            ->limit($perPage)
+            ->get(['id', 'name'])
+            ->toArray();
+    }
+
     /** 단건 */
     public function show(int $id)
     {