Handle AlsoEnergy code 2777 (Solectria Inverter Faults V2) + split benign low-DC standby from real faults

BOLT-2444. 2777 falls through to default in mapAlertCodeToAlertType -> fires Unknown-code Slack webhook + tags UNKNOWN. 2777 is a bucket code: real inverter faults AND benign low-DC standby (Waiting for more power / Low DC power). Add case 2777, discriminate on message: benign standby -> PERFORMANCE_DEGRADED/WAIT_FOR_SOLAR (non-paging), real fault -> HARDWARE_FAULT/INVERTER_FAULT. Add unit tests. Branch cato/bolt-2444-alsoenergy-2777.