feat: 휴가 관리 API 구현 (Phase 1)

- leaves, leave_balances 테이블 마이그레이션 추가
- Leave, LeaveBalance 모델 구현 (BelongsToTenant, SoftDeletes)
- LeaveService 서비스 구현 (CRUD, 승인/반려/취소, 잔여일수 관리)
- LeaveController 및 FormRequest 5개 생성
- API 엔드포인트 11개 등록 (/v1/leaves/*)
- Swagger 문서 (LeaveApi.php) 작성
- i18n 메시지 키 추가 (message.leave.*, error.leave.*)

app/Http/Requests/Leave/StoreRequest.php

@@ -0,0 +1,39 @@
+<?php
+
+namespace App\Http\Requests\Leave;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class StoreRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'user_id' => 'nullable|integer|exists:users,id',
+            'leave_type' => 'required|string|in:annual,half_am,half_pm,sick,family,maternity,parental',
+            'start_date' => 'required|date|after_or_equal:today',
+            'end_date' => 'required|date|after_or_equal:start_date',
+            'days' => 'required|numeric|min:0.5|max:365',
+            'reason' => 'nullable|string|max:1000',
+        ];
+    }
+
+    public function messages(): array
+    {
+        return [
+            'leave_type.required' => __('validation.required', ['attribute' => '휴가유형']),
+            'leave_type.in' => __('validation.in', ['attribute' => '휴가유형']),
+            'start_date.required' => __('validation.required', ['attribute' => '시작일']),
+            'start_date.after_or_equal' => __('validation.after_or_equal', ['attribute' => '시작일', 'date' => '오늘']),
+            'end_date.required' => __('validation.required', ['attribute' => '종료일']),
+            'end_date.after_or_equal' => __('validation.after_or_equal', ['attribute' => '종료일', 'date' => '시작일']),
+            'days.required' => __('validation.required', ['attribute' => '사용일수']),
+            'days.min' => __('validation.min.numeric', ['attribute' => '사용일수', 'min' => 0.5]),
+        ];
+    }
+}