feat(backend): add calculatedAt metric freshness indicator (Closes #1240) - #1350

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, 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/

1 issue was detected with this workflow: CodeQL language 'javascript' is referenced by more than one entry in the 'language' matrix parameter for job 'codeql-analysis'. This may result in duplicate alerts. Please edit the 'language' matrix parameter to keep only one of the following: 'javascript', 'typescript'.