[FEAT] Add compatibility with NIP-99 (Classified Listings) and Gamma Markets spec

[BenGWeeks]

Summary

Add support for NIP-99 Classified Listings to expand marketplace functionality beyond the current NIP-15 implementation.

Background

Diagon Alley currently implements NIP-15 for marketplace functionality (product listings kind 30018, stall information kind 30017). NIP-99 provides a complementary standard for classified listings that would broaden the types of listings supported.

Relevant Specifications

• NIP-99 (Classified Listings): https://github.com/nostr-protocol/nips/blob/master/99.md

  • Defines kind 30402 for classified listings
  • Supports categories, location, pricing, and status tags
  • Designed for general marketplace listings (services, rentals, jobs, etc.)

• Gamma Markets Spec: https://github.com/ArcadeLabsInc/gamma

  • Enhanced marketplace features built on Nostr
  • Additional metadata and filtering capabilities

Proposed Features

• Parse and display NIP-99 classified listings (kind 30402)
• Support NIP-99 tags: title, summary, location, price, status
• Filter by listing type (NIP-15 products vs NIP-99 classifieds)
• Category-based browsing for classified listings
• Compatibility with Gamma Markets enhanced features

Benefits

• Broader marketplace coverage (not just physical products)
• Support for services, rentals, job listings, etc.
• Interoperability with other Nostr marketplace clients