[Feature] Web UI dashboard for task DAG visualization

## Summary Build a web-based dashboard that visualizes the task DAG, agent status, and execution progress in real-time. ## Motivation Multi-agent workflows can be complex. A visual representation would help users: - Understand the task dependency graph at a glance - Monitor which agents are running, waiting, or completed - Debug failures by seeing where the pipeline broke - Demo the framework to stakeholders ## Proposed Approach - Lightweight web server (express or built-in http) serving a single-page app - DAG rendered with a graph library (e.g., D3, dagre, or elkjs) - WebSocket connection for real-time status updates - Display: task nodes with status colors, agent assignments, execution time, token usage ## Design Sketch ``` [Architect: Design API] ──→ [Developer: Implement] ──→ [Reviewer: Review] ✅ Done (2.3s) 🔄 Running ⏳ Waiting ``` ## Open Questions - Ship as a separate package or built-in opt-in? - How much detail to show (full LLM conversation, tool calls, etc.)?