feat(update-modal): display last 5 release notes instead of single

- Modified backend to fetch last 5 releases from GitHub API
- Updated frontend to iterate through and display multiple releases
- Added latest badge and publish date styling
- Added update.latestBadge translation key to all locales
- Maintains backward compatibility for single changelog display

locales/ja.json

@@ -1214,6 +1214,7 @@
         "checkingUpdates": "更新を確認中...",
         "checkingMessage": "最新バージョンを確認しています。お待ちください。",
         "showNotifications": "更新通知を表示",
+        "latestBadge": "最新",
         "updateProgress": {
             "preparing": "更新を準備中...",
             "installing": "更新をインストール中...",