Add status page enhancements and engine improvements

Status page:
- Per-phase grid power (L1/L2/L3) with export/import direction
- Shelly PM live power badge on active wallbox rows
- Compressor power shown below consumer list
- SyncDeviceStates() method on Store for PM power readback

Engine:
- Fix wallbox mutex: re-read Active state after P3 so same-cycle
  WallboxA activation correctly blocks WallboxB in P4
- Fix RecoverState: set ActivatedAt to zero so recovered consumers
  are immediately eligible for shutdown decisions
- Add 3 new unit tests: mutual exclusion, car-not-charging,
  compressor-idle early release

Makefile:
- make install no longer overwrites /etc/ems/ems-config.yaml if it
  already exists (prevents password loss on updates)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

main.go

@@ -184,6 +184,7 @@ func runCycle(
 		logger.Warn("all Shelly devices unreachable, skipping override detection", "error", err)
 	} else {
 		eng.SyncHardwareState(shellyStates, now, cfg.EMS.OverrideTimeoutParsed())
+		store.SyncDeviceStates(shellyStates)
 	}
 
 	// Update metrics with current state