Add llms.txt and KeeperLink GEO profile

[pengshenghai]

Summary

• Add a root llms.txt profile for OpenClaw KeeperLink with canonical links, key entities, answer-first FAQ, and citation guidance.
• Add a short answer-first README intro plus a README pointer/FAQ for generative engines and readers.
• Keep the scope documentation-only and avoid any changes to payment, wallet, settlement, or runtime behavior.

Validation

• git diff --check -- README.md llms.txt passed (only Git's normal Windows LF-to-CRLF working-copy notice appeared).
• rg -n "llms.txt|What is OpenClaw KeeperLink|RustChain|x402|KeeperHub|0G|Gensyn AXL|OpenClaw Audit Envelope|answer-first|production marketplace" README.md llms.txt confirmed the expected GEO terms and caveats are present.
• python %TEMP%\verify_keeperlink_geo.py passed with KeeperLink GEO docs ok.

AI Assistance

This PR was prepared with AI assistance. I reviewed the current README/docs, kept the change to documentation only, and validated the resulting files with the commands above.