Add langgraph-starter-kit to Templates & Starters

[ac12644]

Summary

Adding langgraph-starter-kit to the Templates & Starters section.

What it is: A production-ready multi-agent starter kit for LangGraph (TypeScript) with:

• 6 agent patterns: Supervisor, Swarm, Human-in-the-Loop, Structured Output, Research Agent, RAG
• 5 LLM providers: OpenAI, Anthropic, Google, Groq, Ollama
• MCP tool integration (stdio + HTTP)
• Interactive CLI scaffolder (npx create-langgraph-app)
• Fastify HTTP server with SSE streaming
• LangGraph Studio + LangSmith tracing support
• 25+ tests, GitHub Actions CI, Docker Compose

Fits naturally in the Templates & Starters category alongside the other starter templates.