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/Controllers/Api/V1/ApprovalLineController.php

@@ -0,0 +1,71 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Helpers\ApiResponse;
+use App\Http\Controllers\Controller;
+use App\Http\Requests\Approval\LineIndexRequest;
+use App\Http\Requests\Approval\LineStoreRequest;
+use App\Http\Requests\Approval\LineUpdateRequest;
+use App\Services\ApprovalService;
+use Illuminate\Http\JsonResponse;
+
+class ApprovalLineController extends Controller
+{
+    public function __construct(private ApprovalService $service) {}
+
+    /**
+     * 결재선 목록
+     * GET /v1/approval-lines
+     */
+    public function index(LineIndexRequest $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($request) {
+            return $this->service->lineIndex($request->validated());
+        }, __('message.fetched'));
+    }
+
+    /**
+     * 결재선 상세
+     * GET /v1/approval-lines/{id}
+     */
+    public function show(int $id): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($id) {
+            return $this->service->lineShow($id);
+        }, __('message.fetched'));
+    }
+
+    /**
+     * 결재선 생성
+     * POST /v1/approval-lines
+     */
+    public function store(LineStoreRequest $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($request) {
+            return $this->service->lineStore($request->validated());
+        }, __('message.approval.line_created'));
+    }
+
+    /**
+     * 결재선 수정
+     * PATCH /v1/approval-lines/{id}
+     */
+    public function update(int $id, LineUpdateRequest $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($id, $request) {
+            return $this->service->lineUpdate($id, $request->validated());
+        }, __('message.updated'));
+    }
+
+    /**
+     * 결재선 삭제
+     * DELETE /v1/approval-lines/{id}
+     */
+    public function destroy(int $id): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($id) {
+            return $this->service->lineDestroy($id);
+        }, __('message.deleted'));
+    }
+}