Nostr app handlers

Kind 31990 already lists software that can open Nostr events. ORBSTR reads it. It does not replace it.

NIP-89 is the handler directory: d, k, and platform URL templates. Use it when a service handles Nostr kinds or speaks NIP-90. Use kind 39698 when the service is an MCP tool, model, API, or other agent capability that is not an event handler.