Every starter's route.ts now reads process.env.AGENT_URL as the
primary agent endpoint, with framework-specific vars as fallback:
- AGENT_URL || "http://localhost:8000" (pydantic-ai, adk, agno, crewai,
ms-agent-python, ms-agent-dotnet, strands-python)
- AGENT_URL || LANGGRAPH_DEPLOYMENT_URL || "http://localhost:8123"
(langgraph-python, langgraph-js)
- AGENT_URL || "http://localhost:9000" (llamaindex)
Also adds .env.example with AGENT_URL to all starters.