fix(links): remove fabricated Agent Studio listing CTAs

[JasonColapietro]

What changed

• remove fabricated Agent Studio listing URLs from all 18 deterministic example profiles
• suppress the external listing CTA when an example has no verified live listing
• label the profile data as illustrative while preserving the real add-your-own-agent path
• add link-integrity regressions covering all 18 public detail pages and sitemap entries

Root cause

The deterministic Agentix examples derived Agent Studio URLs from local demo slugs. Those demo records were never published in Agent Studio, so every public detail CTA pointed to a 404.

Impact

All 18 public example profiles remain useful as illustrative tracker data without claiming a live x402 listing that does not exist. Operator-entered agents can still retain a real listing URL.

Validation

• reproduced all 18 current CTA destinations as first-hop 404s
• checked the current 29-entry Agent Studio production catalog; none of the 18 illustrative Agentix profiles has an exact published match
• git diff --check
• Vercel remote preview build will gate merge