Paginated job history grouped by session. See spec §6.1.

Phase C v1 limitations:

• search matches label and customer_id only (error_message is not searchable server-side — would require a second pass post-fan-out, deferred).
• customer_label is not returned (no source table for human-readable customer names today — frontend renders raw customer_id; tracked as Phase C+ enhancement).
• No cursor pagination — endpoint returns all rows in the since_days window. Acceptable for current volumes; add cursor if rows-per-page exceeds ~200.