Refactor agents app: flat API, client-side grouping, unified agent view
Server now returns flat {runs, agents, facets} data. All grouping,
sorting, and aggregation moved to frontend. Shows all agents (generators
and tool agents) unified with capability badges, descriptions, color
accents, model info, error previews, and day summary bar.
- Expand _parse_agent_events() with model and error_message extraction
- Add _build_agents_meta() loading all muse configs (not just tool agents)
- Restructure api_agents_day() to return flat data + metadata
- Remove redundant api_agent_runs() endpoint and _group_agents_by_name()
- Rewrite workspace.html with client-side grouping and rich card UI
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>