FR: blocking convenience wrapper for the AI job flow

[aaguileraruiz]

Add ask_job_blocking(client, model_id, prompt, topic_name=None) to helpers.py in #20, mirroring wait_query_blocking's existing shape for the query path. Submit → poll → fetch result → return one finished answer. No caller should have to see a jobId to use this, on either path. @jdavidson