Add arkhia facilitator

[sami-bcw]

Description

Adds Arkhia as a Facilitator in the x402 ecosystem.

• Includes metadata for Arkhia Facilitator
• Networks, schemes, and assets are based on the live /supported endpoint
• Adds logo to /public/logos/arkhia.png

Tests

No code changes.

• Verified metadata structure matches existing facilitator entries
• Confirmed networks and schemes via /supported endpoint
• Ran site locally to ensure the facilitator renders correctly

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

[vercel]

@sami-bcw is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.