[#5][#6] Add AI pipeline timing budget + Prometheus stale-metric guard

[alan237740261-crypto]

Two bounties in one:\n\n## [#6] Add Prometheus stale-metric guard ($25)\n- Added --stale-threshold option to health_check.py\n- Stale metrics flagged as STALE when last check exceeds threshold\n\n## [#5] Add AI pipeline timing budget summary ($25)\n- Per-stage elapsed time recorded\n- End-of-pipeline timing budget summary table

[zhaog100]

/claim

I'll implement this bounty task.

[Soengkit]

Thanks for the PR. I am closing this because Soengkit/zeroeye is only my working fork of the upstream repository, not an official bounty intake or payment queue. The fork parent/source is NemoMi/zeroeye: https://github.com/NemoMi/zeroeye. Please use the upstream owner current process for any submission or claim, and do not post payment details here.