feat: add Xpay facilitator

[sriakula1]

Add Facilitator

Summary

• Facilitator Name: Xpay
• URL: https://facilitator.xpay.sh
• Website: https://xpay.sh
• Twitter: @xpaysh
• Short description: Non-custodial x402 facilitator on Base, with OpenAPI and .well-known/x402 discovery endpoints

Required changes

• Added config file at packages/facilitators/src/facilitators
• Exported in packages/facilitators/src/facilitators/index.ts
• Appended to packages/facilitators/src/lists/all.ts
• Chose a new unique color not used by other facilitators
• Updated README.md with a one-line entry under Facilitators
• dateOfFirstTransaction is correct and matches on-chain history
• Facilitator has at least 10 USDC transfers
• Added image to apps/scan/public
• Make sure we support that chain
• Make sure all EVM addresses are lowercase

[vercel]

@sriakula1 is attempting to deploy a commit to the Merit Systems Team on Vercel.

A member of the Team first needs to authorize it.