refactor(server): remove legacy scheduler code [p2] - #3244

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-java@v3, github/codeql-action/analyze@v3, github/codeql-action/autobuild@v3, github/codeql-action/init@v3. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Cannot build an overlay database because build-mode is set to "undefined" instead of "none". Falling back to creating a normal full database instead.

CodeQL Action v3 will be deprecated in December 2026. Please update all occurrences of the CodeQL Action in your workflow files to v4. For more information, see https://github.blog/changelog/2025-10-28-upcoming-deprecation-of-codeql-action-v3/

setup-java v3 is deprecated and will no longer receive updates. Please migrate to actions/setup-java@v5.