Addresses "I have to configure MQTT per device; HA just works":
- Shared device account `shelly` (one credential every Shelly uses) with a
SCOPED ACL (status/events/online/rpc for any prefix; cannot touch homeos/,
ring/ or $SYS). gen-passwd seeds it from MQTT_SHELLY_PASSWORD.
- Auto-onboarding: IngestShellyMessage creates the device on the first
recognizable component (sys/wifi/cloud noise ignored), so pointing a Shelly
at the broker is all it takes — no manual "Zuweisen". Partial unique index on
config->>'mqtt_prefix' + race-safe create (merge-dedup migration).
- Settings → Geräte-MQTT card: server, username, reveal/copy password + steps
(config/homeos.php, MQTT_DEVICE_HOST). Discovery "Zuweisen" now upserts by
prefix (names/rooms an already-onboarded device, no duplicate) and no longer
forces per-device creds.
- Per-device credentials kept as opt-in hardening: a "generate" button on the
device page (pattern %u ACL retained).
Live-verified: publishing as `shelly` to a new prefix auto-creates the device
with switch+power state; a sys topic creates nothing. Suite 46 green, 12/12
tabs clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>