docs: add Peer fiat off-ramp module

[ADWilkinson]

Summary

• add the published wdk-protocol-fiat-peer community module to the fiat, all-module, and community catalogs
• describe the supported surface precisely: Base USDC off-ramp, live fiat estimates, and unsigned transaction preparation
• mark the module as community-owned and link its package, source, and usage documentation

Module evidence

• npm: https://www.npmjs.com/package/wdk-protocol-fiat-peer
• source and documentation: https://github.com/zkp2p/wdk-protocol-fiat-peer
• implements WDK IFiatProtocol; 8 tests plus TypeScript, ESM, CJS, and package-export validation pass in the module repository

Validation

• npm run check:meta
• npm run check:links (0 errors; existing external warnings only)
• git diff --check
• npm run build was not run: installing the docs dependencies requires authenticated access to Tether's private @tetherto/docs-seo-* GitHub Packages, which is unavailable to this external fork.