Trigger Run Pipeline

Kick off run_ttab_pipeline.py in a DETACHED subprocess.

Returns immediately with the PID + log path. The pipeline can take well over 10 minutes (enrichment + materialization + training), so we cannot block. Poll /v1/cron/data-status to see progress, or /v1/verify to see when opposition_risks turns non-null.

Resilient to HTTP timeouts — the subprocess is fully detached from the request lifecycle (start_new_session=True), so even if the client disconnects, the pipeline keeps running.