The declarative-gen-ui demo across the three langgraph integrations now
relies on the middleware to inject and execute generate_a2ui — the agents
collapse to create_agent + CopilotKitMiddleware with no hand-rolled tool.
Adds render_a2ui fixtures for the new tool path and pins the integrations
to the A2UI alpha SDKs (copilotkit 0.1.94a1, @copilotkit/sdk-js 1.59.3-alpha.1).
Adds per-integration D6 fixtures for langgraph-python, langgraph-typescript,
and langgraph-fastapi. Each fixture is keyed by match.context for cross-
integration isolation and uses hasToolResult:false on toolCall responses
to prevent re-match loops.