ecosystem: add AAAA-Nexus — hosted AI infrastructure with x402 payments

[atomadictech]

Summary

Adding AAAA-Nexus to the x402 ecosystem.

Why it belongs

• hosted AI infrastructure with x402 pay-per-call access
• public API at https://aaaa-nexus.atomadictech.workers.dev
• hosted MCP endpoint at /mcp
• public repo: https://github.com/atomadictech/aaaa-nexus
• agent card: https://aaaa-nexus.atomadictech.workers.dev/.well-known/agent.json

This updates the submission to the current approved public positioning and removes older naming from the ecosystem entry.

[atomadictech]

Updated this submission to the current public positioning.

Current public surface:

• AAAA-Nexus
• public repo: https://github.com/atomadictech/aaaa-nexus
• hosted API / agent card / MCP endpoint at https://aaaa-nexus.atomadictech.workers.dev
• MCP package: atomadic-helix-mcp

The PR branch, partner metadata, and description now reflect the corrected naming and scope.

[atomadictech]

Correction: the MCP package/install name should read aaaa-nexus-mcp.