#777 Dashboard UX: agent_leaf child runs show as 'leaf' and clutter the run list (should show run name + nest under parent)

Research campaigns spawn N child agent_leaf runs. Backend data is correct: each child workflow_run.workflow_name = agent_leaf_<subgoal> (e.g. agent_leaf_python), tags.subgoal_name set, parent_run_id set, all sharing the agent_leaf definition. But the dashboard shows them as 'leaf' because that is the agent_leaf DSL's single task id (builder.task('leaf',...)), surfaced as activity_name on the auto-activity. Two fixes: (1) display run workflow_name (or tags.subgoal_name) instead of the task/activity name in the views that show 'leaf'; (2) child runs should nest under their parent agent_research run (parent_run_id) or be filtered from the top-level list. Backend enabler needed: GET /api/v1/workflows list does not currently return parent_run_id and has no top_level filter - add both. Needs a dashboard (SvelteKit) change + redeploy; get a screenshot of the exact view first. Surfaced during #771 agentic verification.