feat: Phase 3.8 바로빌 세금계산서 연동 API 구현

- 마이그레이션: barobill_settings, tax_invoices 테이블 생성
- 모델: BarobillSetting (인증서 암호화), TaxInvoice (상태/유형 상수)
- 서비스: BarobillService (API 연동), TaxInvoiceService (CRUD, 발행/취소)
- 컨트롤러: BarobillSettingController, TaxInvoiceController
- FormRequest: 6개 요청 검증 클래스
- Swagger: API 문서 완성 (BarobillSettingApi, TaxInvoiceApi)

app/Http/Requests/TaxInvoice/CancelTaxInvoiceRequest.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace App\Http\Requests\TaxInvoice;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class CancelTaxInvoiceRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'reason' => ['required', 'string', 'max:500'],
+        ];
+    }
+
+    public function attributes(): array
+    {
+        return [
+            'reason' => __('validation.attributes.cancel_reason'),
+        ];
+    }
+}