feat: [approval] 전자결재 모듈 API 구현

- 마이그레이션 4개 (approval_forms, approval_lines, approvals, approval_steps)
- 모델 4개 (ApprovalForm, ApprovalLine, Approval, ApprovalStep)
- ApprovalService 비즈니스 로직 (양식/결재선 CRUD, 기안함/결재함/참조함, 결재 액션)
- 컨트롤러 3개 (ApprovalFormController, ApprovalLineController, ApprovalController)
- FormRequest 13개 (양식/결재선/문서 검증)
- Swagger 문서 3개 (26개 엔드포인트)
- i18n 메시지/에러 키 추가
- 라우트 26개 등록

app/Http/Requests/Approval/FormUpdateRequest.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace App\Http\Requests\Approval;
+
+use App\Models\Tenants\ApprovalForm;
+use Illuminate\Foundation\Http\FormRequest;
+
+class FormUpdateRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        $categories = implode(',', ApprovalForm::CATEGORIES);
+
+        return [
+            'name' => 'nullable|string|max:100',
+            'code' => 'nullable|string|max:50|regex:/^[a-zA-Z0-9_-]+$/',
+            'category' => "nullable|string|in:{$categories}",
+            'template' => 'nullable|array',
+            'template.fields' => 'required_with:template|array',
+            'template.fields.*.name' => 'required_with:template.fields|string|max:50',
+            'template.fields.*.type' => 'required_with:template.fields|string|in:text,textarea,number,date,select,checkbox,file',
+            'template.fields.*.label' => 'required_with:template.fields|string|max:100',
+            'template.fields.*.required' => 'nullable|boolean',
+            'template.fields.*.options' => 'nullable|array',
+            'is_active' => 'nullable|boolean',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'code.regex' => __('validation.regex', ['attribute' => '양식코드']),
+        ];
+    }
+}