feat: 인앱 업데이트 체크 API 구현

- app_versions 테이블 마이그레이션 (시스템 레벨, tenant_id 없음)
- AppVersion 모델 (SoftDeletes)
- AppVersionService: getLatestVersion, downloadApk
- AppVersionController: GET /api/v1/app/version, GET /api/v1/app/download/{id}
- ApiKeyMiddleware 화이트리스트에 api/v1/app/* 추가
- app_releases 스토리지 디스크 추가

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

routes/api.php

@@ -38,6 +38,7 @@
     require __DIR__.'/api/v1/documents.php';
     require __DIR__.'/api/v1/common.php';
     require __DIR__.'/api/v1/stats.php';
+    require __DIR__.'/api/v1/app.php';
 
     // 공유 링크 다운로드 (인증 불필요 - auth.apikey 그룹 밖)
     Route::get('/files/share/{token}', [FileStorageController::class, 'downloadShared'])->name('v1.files.share.download');

routes/api/v1/app.php

@@ -0,0 +1,16 @@
+<?php
+
+use App\Http\Controllers\Api\V1\AppVersionController;
+use Illuminate\Support\Facades\Route;
+
+/*
+|--------------------------------------------------------------------------
+| App Version Routes (앱 버전 관리)
+|--------------------------------------------------------------------------
+| 인앱 업데이트용 API (Bearer 토큰 불필요, API Key만 필요)
+*/
+
+Route::prefix('app')->group(function () {
+    Route::get('/version', [AppVersionController::class, 'latestVersion']);
+    Route::get('/download/{id}', [AppVersionController::class, 'download']);
+});