fix(settings): stop telling people the webhook URL must be public

A notification target on a private network has been reachable since the
operator allowlist for private origins arrived; the hint under the URL
field and the guide still said the address had to be public.

docs/self-hosting/notifications.md

@@ -191,7 +191,7 @@ and surface on the lock screen.
 
 The generic webhook POSTs every enabled event as JSON to a URL you own —
 wire it into your own automation (Home Assistant, n8n, a Discord/Slack
-relay, whatever routes the payload). You supply a public URL and,
+relay, whatever routes the payload). You supply the URL and,
 optionally, one custom header (e.g. an auth token).
 
 1. In HealthLog open `/settings/notifications`, fill the Webhook card's