feat: SHA-256 完整性校验体系（端点/下载头/验证页/元数据+GitHub digest 校验）、验证页状态图标、tls_skip_verify 开关 - #20

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-go@v5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/