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/Services/AppVersionService.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace App\Services;
+
+use App\Models\AppVersion;
+use Illuminate\Support\Facades\Storage;
+use Symfony\Component\HttpFoundation\StreamedResponse;
+
+class AppVersionService
+{
+    /**
+     * 최신 버전 확인
+     */
+    public static function getLatestVersion(string $platform, int $currentVersionCode): array
+    {
+        $latest = AppVersion::where('platform', $platform)
+            ->where('is_active', true)
+            ->whereNotNull('published_at')
+            ->orderByDesc('version_code')
+            ->first();
+
+        if (! $latest || $latest->version_code <= $currentVersionCode) {
+            return [
+                'has_update' => false,
+                'latest_version' => null,
+            ];
+        }
+
+        return [
+            'has_update' => true,
+            'latest_version' => [
+                'id' => $latest->id,
+                'version_code' => $latest->version_code,
+                'version_name' => $latest->version_name,
+                'release_notes' => $latest->release_notes,
+                'force_update' => $latest->force_update,
+                'apk_size' => $latest->apk_size,
+                'download_url' => url("/api/v1/app/download/{$latest->id}"),
+                'published_at' => $latest->published_at?->format('Y-m-d'),
+            ],
+        ];
+    }
+
+    /**
+     * APK 다운로드
+     */
+    public static function downloadApk(int $id): StreamedResponse
+    {
+        $version = AppVersion::where('is_active', true)->findOrFail($id);
+
+        if (! $version->apk_path || ! Storage::disk('app_releases')->exists($version->apk_path)) {
+            abort(404, 'APK 파일을 찾을 수 없습니다.');
+        }
+
+        // 다운로드 수 증가
+        $version->increment('download_count');
+
+        $fileName = $version->apk_original_name ?: "app-v{$version->version_name}.apk";
+
+        return Storage::disk('app_releases')->download($version->apk_path, $fileName);
+    }
+}