API Server - Add `has_ended` to the response of PieplineRunsService.list

[Ark-kun]

Add has_ended: bool | None to PipelineRunResponse which is set when list(..., include_execution_stats == True)

[maxy-shpfy]

🤖 Auto-triage assigned priority P3

The issue describes an enhancement to add a new field to an API response, which does not impact the core functionality or user experience directly. It is a minor improvement that does not align with urgent or regular project priorities.

Key factors:
• minor enhancement
• no user impact
• not part of urgent or regular project

📋 P3 Priority: Nice-to-have or future work.

This priority was determined by AI analysis with 90% confidence.

[yuechao-qin]

Started, this is low priority so putting it back in the backlog for now:

https://app.graphite.com/github/pr/TangleML/tangle/94