fix: avoid crash when forcing app close during download (#59) 

feat: improve `fetch_lesson_list` Signed-off-by: 晨叶梦春 <wuziqian211@126.com>

fix: 保护无控制台运行时的错误输出，优化下载失败信息展示 

refactor: 优化代码规范以及跨平台兼容性 - 改善跨平台 UI/系统处理 - 规范类型注解，消除 Pylance 非致命警告

修复Mac app无法正常打开 (#53) * Update build-release.yml

Merge pull request #51 from Mister-Hope/main feat: add support for mac gui app

fix(README): issue link 

fix(spec): support non-Windows platform 

Update README.md 

Update .gitignore