feat(API): Position API 추가 (직급/직책 통합)

- Position 모델 생성 (type: rank | title)
- PositionService: CRUD + reorder 구현
- PositionController: REST API 엔드포인트
- Swagger 문서 작성 (PositionApi.php)
- 마이그레이션: positions 테이블 + common_codes 등록
- routes/api.php에 라우트 등록

Phase L-3 (직급관리), L-4 (직책관리) 백엔드 완료

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Http/Requests/PositionReorderRequest.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace App\Http\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class PositionReorderRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'items' => 'required|array|min:1',
+            'items.*.id' => 'required|integer|exists:positions,id',
+            'items.*.sort_order' => 'required|integer|min:0',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'items.required' => __('validation.required', ['attribute' => '항목']),
+            'items.*.id.required' => __('validation.required', ['attribute' => 'ID']),
+            'items.*.id.exists' => __('validation.exists', ['attribute' => 'ID']),
+            'items.*.sort_order.required' => __('validation.required', ['attribute' => '정렬순서']),
+        ];
+    }
+}