Ported from the upstream PR (lnbits/nostrclient#74, idea from #68).
Nothing will ever serve a subscription when nostrclient has no relay
at all, so refuse it per NIP-01 instead of registering it silently.
Keyed on "no relay configured" rather than "none connected": a
configured relay that is merely reconnecting gets the cached
subscription replayed, so refusing the REQ there would be a regression.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013Tbyw6FwjhEJg3gHfPHxWt
