POST /notifications/app-message delivers an app's message to every channel
with the new "Messages from connected apps" switch on (off by default),
through quiet hours, the digest and the log. API keys need the new "Send
notifications" permission, and their owner notifications:update; plain text,
http(s) links, 20 messages a minute per key. The electricity-price door and
this one now share one scoped-key check. /queue?batch=<id> opens and
highlights one batch order.
