The HA Companion app needs an external_url for clickable notification
deep-links to resolve when the phone is off the home Wi-Fi. Reach is via
Tailscale (Headscale tailnet solar.internal), so external_url points at
the FQDN jupiter.solar.internal:8123; internal_url stays on the bare
hostname for LAN-attached devices.
Phase A only: device registration + notify group + smoke-test land in a
follow-up commit once Companion has registered real mobile_app_<slug>
service names. See docs/superpowers/specs/2026-05-18-ha-push-notifications.md.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
marthsincemelee