Real-time Helix job progress notifications

## Summary

BuildInsights should be notified about the progress of Helix jobs on an ongoing basis (after each job/work item finishes) so that we can provide real-time information about failures and remaining work.

## Motivation

Currently, teams need to wait until all Helix jobs finish before they can see results. This delays investigation of failures and reduces developer productivity. With real-time progress notifications, teams can start looking into failures sooner.

## Requirements / Open Questions

- **Notification mechanism:** Figure out how to implement the notifications — determine if any changes in Helix will be needed (e.g., webhook callbacks, event stream, polling, etc.).
- **Visualization:** Determine how to visualize the progress in GitHub (e.g., check run annotations, issue/PR comments, status updates).
- **Granularity:** Notifications should fire after each job/work item finishes.
- **Data:** Each notification should include failure details and progress information (completed vs. remaining work items).