Add SelectaRank gateway, MCP server and x402-conformance to Projects

[maokao96]

Adds three entries to Projects.md: the pay-per-call data gateway (https://selectarank-data.vercel.app, Base USDC), its MCP server, and the x402-conformance checker. Prices are the public values; no sales figures are claimed.

This PR was prepared by an AI coding agent (Claude Code) on behalf of the maintainer, Ryoya Tosaka (SelectaRank). The listing text states only verifiable facts; there are no sales to date.

[github-actions]

Projects.md URL check failed

This pull request adds URLs to Projects.md that are not allowed. The same rules are enforced by the server when an endpoint is registered:

• URLs whose host is an IP address are not allowed.
• URLs whose host contains an IP-like pattern (e.g. 204-168-208-32) are not allowed.
• URLs whose host contains a blocked domain are not allowed (netlify, trycloudflare, workers.dev, pages.dev, vercel.app, sslip.io, ts.net).

Rejected URLs:

• https://selectarank-data.vercel.app - the host selectarank-data.vercel.app contains the blocked domain vercel.app
• https://selectarank-data.vercel.app/openapi.json - the host selectarank-data.vercel.app contains the blocked domain vercel.app

Please update Projects.md to only use allowed, publicly resolvable domains. This pull request is being closed automatically.