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>

app/Http/Controllers/Api/V1/AppVersionController.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Http\Controllers\Controller;
+use App\Services\AppVersionService;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Symfony\Component\HttpFoundation\StreamedResponse;
+
+class AppVersionController extends Controller
+{
+    /**
+     * 최신 버전 확인
+     * GET /api/v1/app/version?platform=android&current_version_code=1
+     */
+    public function latestVersion(Request $request): JsonResponse
+    {
+        $platform = $request->input('platform', 'android');
+        $currentVersionCode = (int) $request->input('current_version_code', 0);
+
+        $result = AppVersionService::getLatestVersion($platform, $currentVersionCode);
+
+        return response()->json([
+            'success' => true,
+            'data' => $result,
+        ]);
+    }
+
+    /**
+     * APK 다운로드
+     * GET /api/v1/app/download/{id}
+     */
+    public function download(int $id): StreamedResponse
+    {
+        return AppVersionService::downloadApk($id);
+    }
+}