v0.5.0：手动更新、可靠安装、完整提醒
现在可以在应用内主动掌握更新时间，同时保留原有的自动更新保障。
🎉 新功能
- 设置页新增“软件更新”板块。可以随时检查正式版更新，查看最新版本、发布日期和官方发布说明，再自行决定何时下载。
- 检查到新版本后，更新流程会按“下载更新 → 安装并重启”分步进行。下载进度会持续显示，安装前仍会再次确认，避免误触导致应用突然退出。
- 自动更新继续在后台提供兜底。如果更新已经由后台开始下载，设置页会直接显示同一份进度，不会重复下载。
✨ 改进
- 主动检查现在会明确显示“已是最新版”或网络暂时不可用，并记录最近检查时间。
- 下载、校验和安装失败会提供对应的重试入口，已下载好的有效更新不会因再次检查而丢失。
🐛 Bug 修复
- 修复 macOS 上旧更新暂存目录包含特殊应用文件时，点击“立即升级并重启”没有反应的问题。现在会可靠清理旧暂存内容；清理失败时也会明确提示，而不是静默停住。
- 再平衡提醒继续使用 5% 偏离阈值，但不再只展示前六项。所有超过阈值的项目都会完整显示。
You can now choose when to check, download, and install updates while keeping the existing automatic-update safety net.
🎉 New features
- Settings now includes a Software Update section. You can check for stable releases at any time, review the latest version, publication date, and official release notes, then decide when to download.
- Available updates follow a clear “Download update → Install and restart” flow. Download progress remains visible, and installation still requires confirmation so an accidental click will not suddenly close the app.
- Automatic updates continue to work in the background. If a background download is already running, Settings shows the same progress instead of starting a duplicate download.
✨ Improvements
- Manual checks clearly report whether the app is current or the update service is temporarily unavailable, together with the most recent check time.
- Download, validation, and installation failures now provide the appropriate retry action, and a valid downloaded update is preserved across later checks.
🐛 Bug fixes
- Fixed “Install and restart” appearing unresponsive on macOS when an older update staging folder contained special application files. The app now clears stale staging content reliably and shows an actionable error if cleanup fails.
- The rebalance threshold remains 5%, but the Overview no longer stops after six alerts. Every item beyond the threshold is now displayed.