Fix link for facilitators in x402 documentation

[aminamos]

Summary

Fixed the x402 facilitator link so it points to the correct documentation / current facilitator guidance.

Documentation checklist

https://developers.cloudflare.com/agents/tools/payments/x402/

• Is there a changelog entry?
  • No, this is a small docs/link correction, not a notable product change. Cloudflare’s changelog is for notable changes.
• The change adheres to the documentation style guide.
  • Yes.
• If a larger change, an issue has been opened.
  • No, this is a small link fix.
• Files which have changed name or location have been allocated redirects.
  • No, no file move/rename.

The docs I checked are:

• https://developers.cloudflare.com/style-guide/
• https://developers.cloudflare.com/style-guide/documentation-content-strategy/content-types/changelog/

[cloudflare-docs-bot]

Review

✅ No issues found in commit e99f822.

Code Review

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Conventions

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Style Guide Review

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