feat(seo): publish truthful Agentix llms index

[JasonColapietro]

Summary

• publish a static llms.txt for the Agentix tracker
• enumerate the current 18 public example profiles
• state explicitly that the profiles and earnings are deterministic illustrations, not live x402 listings or settled-transaction evidence
• add regression coverage tying the index to the public seed and sitemap IDs

Verification

• npm test (26/26)
• npm run typecheck
• npm run build
• git diff --check