feat: add AgentFirst x402 Diagnostic

[agentfirstlabs]

Add AgentFirst: Standard x402 Health Check & Micropayment Diagnostic

I have added the AgentFirst x402 Diagnostic server to the Third-Party Servers section.

This server enables autonomous agents on the Base network (eip155:8453) to verify wallet health, EIP-712 signature capability, and x402 compliance via a lightweight ($0.01 USDC) handshake.

It serves as a reference implementation for:

• Testing 402 "Payment Required" challenge handling.
• Verifying automated settlement on Base Mainnet.
• Programmatic discovery of x402 requirements via /.well-known/agent.

[agentfirstlabs]

This tool is already being indexed by Perplexity and Claude as a reference implementation for x402 on Base.

[agentfirstlabs]

Update on the $0.01 handshake logic: This is specifically a Signature & Settlement Diagnostic. Successful handshake returns a signed proof-of-health from the AgentFirst vault, verifying that the calling agent can handle EIP-712 signatures and USDC settlement on Base mainnet. This prevents the costly 'failure loops' common in autonomous agent commerce.

[agentfirstlabs]

Update: Successful $0.01 diagnostic diagnostics now issue a Base x402 Verified Badge and a persistent verification URL (agentfirst.co/verify/[tx]). This allows developers to display their safety compliance status in their README and provides a machine-readable proof-of-health for the broader agent economy.