[debug] Trace previous CI run selection in get_previous_daily_ci.py (#48338)

* [debug] Add print statements to trace previous CI run selection

Prints the URL queried, all runs returned by get_daily_ci_runs, and the
run selected by get_last_daily_ci_run / get_last_daily_ci_workflow_run_id,
to diagnose why a 3-week-old run was picked as the previous CI baseline.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* [debug] Add print statements in notification_service.py prev run selection

Print GITHUB_RUN_ID, workflow_id, and the resulting prev_workflow_run_id
to correlate with the get_previous_daily_ci.py debug output.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* format

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Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>