Use generated docs in local circuit prompt

[arbazkhan971]

Summary

• Fetch https://docs.tscircuit.com/ai.txt and include it in the local circuit system prompt before the existing hand-written API overview.
• Keep the generated docs fetch optional so prompt creation still works if that endpoint is temporarily unavailable.
• Add a mocked-fetch regression test for the generated docs section.
• Skip OpenAI-backed tests when OPENAI_API_KEY is not configured, so fork PR CI can run the non-AI suite without secrets.

/claim #45

Testing

• bun run format
• bun test --timeout 50000
• bunx tsc --noEmit
• bun run build