fix(scheduler): reject past one-time 'at' cron schedules - #1526

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. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Add the `Third-party origin:` field to make review intent explicit.

Add the `Maintainer live check:` field to make review intent explicit.

Add the `Release note:` field to make review intent explicit.

Add the `Linked issue:` field to make review intent explicit.

Add the `Target exception:` field to make review intent explicit.

Add the `Base branch:` field to make review intent explicit.