Add Vercel AI SDK adapter

[hidai25]

Why

The Vercel AI SDK is one of the most common ways teams ship agents today, especially TypeScript/Next.js shops. It's the most-requested missing framework in our adapter list.

EvalView currently has adapters for HTTP, Anthropic, OpenAI, LangGraph, CrewAI, Pydantic AI, Aider, Goose, MCP, and more — see evalview/adapters/. Vercel AI is the gap.

What

Add evalview/adapters/vercel_ai_adapter.py that wraps a Vercel AI SDK agent endpoint (or local script invocation) and produces the same AgentResult shape every other adapter returns.

Acceptance criteria

• New adapter file following the AgentAdapter ABC in evalview/adapters/base.py
• Registered in evalview/adapters/registry.py
• Tool calls + final output captured and round-tripped through the diff engine
• At least one integration test under tests/adapters/ mirroring the existing adapter tests
• README adapter table updated

Hints

• Look at anthropic_adapter.py and openai_assistants_adapter.py for the closest patterns.
• Tool calls in the Vercel AI SDK live on the streamed response — capture them into the trace as they arrive.

Size

~1-2 hours for someone who's used the Vercel AI SDK before.