Fix some specs, improve config

Allow empty string to unset nostr relay URL config

app/controllers/well_known_controller.rb

@@ -4,7 +4,7 @@ class WellKnownController < ApplicationController
   def nostr
     http_status :unprocessable_entity and return if params[:name].blank?
     domain = request.headers["X-Forwarded-Host"].presence || Setting.primary_domain
-    relay_url = Setting.nostr_relay_url
+    relay_url = Setting.nostr_relay_url.presence
 
     if params[:name] == "_"
       # pubkey for the primary domain without a username (e.g. kosmos.org)