fix: 修复课堂 ASR 链路故障（降级链断裂 / Redis 未连接 / 音频静音无回退） - #5

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, dorny/paths-filter@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/