fix(backend): address issues #249, #250, #251, #252 - #439

Error: Multiple versions of pnpm specified: - version 10 in the GitHub Action config with the key "version" - version pnpm@10.28.0 in the package.json with the key "packageManager" Remove one of these versions to avoid version mismatch errors like ERR_PNPM_BAD_PM_VERSION

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/upload-artifact@v4, pnpm/action-setup@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

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