Surface workflow-diagnostic session events (warnings and errors from
Agent Framework workflows) in the turn-event log of the Activity Panel.
- Add workflow-diagnostic case to formatTurnEventEntry with label/detail
formatting that includes executor ID, subworkflow ID, exception type,
and diagnostic message when present
- Add AlertTriangle icon for diagnostic events with error/warning color
- Add 5 tests covering executor-failed, workflow-warning, subworkflow-error,
workflow-error, and missing diagnosticKind fallback
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>