[WIP] Build production-quality Next.js frontend for RTL Design Agent

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Build a production-quality Next.js frontend for an RTL Design Agent.

References:

• @UI_DESIGN_REQUIREMENTS.md - Complete design spec & requirements
• @gradio_app.py - Current implementation (migrate ALL features from this)

Requirements:

• Follow industry best practices (how ChatGPT/Claude are built)
• Complete ALL 6 phases from the design doc
• Use standard patterns: Next.js 14 App Router, TypeScript, Tailwind, shadcn/ui, Zustand, Vercel AI SDK
• FastAPI backend with WebSocket streaming for the existing LangGraph agent
• DO NOT modify existing Python agent code in /src - only create api.py wrapper

Deliverables:

1. /frontend - Next.js app with 3-panel Claude-style layout (collapsible sidebar, chat, artifacts)
2. api.py - FastAPI server exposing existing agent via REST + WebSocket
3. Full feature parity with gradio_app.py: sessions CRUD, streaming chat, tool call display, spec/code/waveform/report viewers

Build this the way a senior engineer at Vercel or Anthropic would - clean architecture, proper error handling, typed throughout.

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