Frontend Tools Setup

Frontend tools registered with `useFrontendTool` arrive in the AG-UI run
input. Convert each AG-UI tool definition into an Anthropic Messages API
tool schema before calling the model. Runs that carry frontend tools use
the direct Messages API path rather than the Claude Agent SDK.

<DemoCode
  file="src/agents/agent.py"
  region="frontend-tools-setup"
  highlight="23-29"
/>