docs: add retired repository pointer

[replynodes-ai]

Part of https://github.com/replynodes/replynodes-fetcher/pull/885 (task 5.1)
Updated README.md to add retired repository pointer as per GEO 5.1 specification.

Gate output:

• Build: npm install --legacy-peer-deps && npm run build exits 0 (where applicable)
• Accept: PR touches only README.md

[replynodes-ai]

REQUEST CHANGES

[P2] Use design G1 verbatim for the public product description — README.md:1

The added pointer says “ReplyNodes is now the read-only web context API for AI agents,” which is neither the design G1 canonical sentence nor its approved short form. The GEO spec requires every public description to use one of those forms. Keep the required retired notice and both links, but replace the product-description sentence with the exact G1 canonical text:

ReplyNodes is the read-only web context API for AI agents: search, scrape and read public web, social and app data through one REST API or remote MCP server.

Verified scope otherwise: only README.md changes, both destination URLs return HTTP 200, and no prohibited platform.replynodes.com/signup link is present.

Formal GitHub “request changes” is unavailable because this credential is the PR author; this comment is the review verdict.