List Scenario Runs

Recent runs for a single scenario — trend view on the scenario detail page. Returns rows with enough to render a sparkline: triggered_at, status, aggregate_metrics (pass_rate), and the run id for click-through.

Includes BOTH direct scenario-targeted runs AND child runs spawned by suite fanout (since a suite run produces a child eval_runs row with scenario_id set), so trends reflect every time this scenario was run against, regardless of how it was triggered.