Upgrade Vercel AI SDK to v6 for pydantic-ai >= 1.49.0 compatibility

[dsfaccini]

Summary

Streaming tool calls fail when using pydantic-ai >= 1.49.0 with this chat UI due to Vercel AI SDK v5 rejecting the new providerMetadata key.

Background

PR pydantic-ai#4127 introduced providerMetadata in tool call responses. Vercel AI SDK v5 does not recognize this key and throws an error, breaking streaming tool calls.

See: pydantic-ai#4163

Current State

"ai": "^5.0.123"

Required Change

Upgrade to Vercel AI SDK v6, which supports the providerMetadata key.