hiit: Add new High Intensity Interval Training app - #2401

On December 2, 2026, GitHub will restrict `pull_request_target` on public repositories by default. To continue allowing the event trigger, configure an Actions policy. Learn more: https://gh.io/securely-using-pull_request_target#default-policy-for-pull_request_target

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: dawidd6/action-download-artifact@bd10f381a96414ce2b13a11bfa89902ba7cea07f, fountainhead/action-wait-for-check@297be350cf8393728ea4d4b39435c7d7ae167c93, peter-evans/create-or-update-comment@5adcb0bb0f9fb3f95ef05400558bdb3f329ee808, peter-evans/find-comment@81e2da3af01c92f83cb927cf3ace0e085617c556. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/