feat: Learning Sites picker (multi-instance switching UI) - #683

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@6f8efc29b200d32929f49075959781ed54ec270c, actions/cache@v3, actions/checkout@v3, github/codeql-action/upload-sarif@458d36d7d4f47d0dd16ca424c1d3cda0060f1360. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/