Use PSU SDR sum for system power chart when available

DCMI reports only the managed power domain (~CPU+MB), missing GPU draw.
PSU AC input sensors cover full wall power. When samplePSUPower returns
data, sum the slots for PowerW; fall back to DCMI otherwise.

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

audit/internal/platform/live_metrics.go

@@ -64,12 +64,20 @@ func SampleLiveMetrics() LiveMetricSample {
 		}
 	}
 
-	// System power — returns 0 if unavailable
-	s.PowerW = sampleSystemPower()
-
 	// Per-PSU power — populated when IPMI SDR has Power Supply entities with Watt readings
 	s.PSUs = samplePSUPower()
 
+	// System power: prefer sum of PSU AC inputs (full wall draw); fall back to DCMI.
+	if len(s.PSUs) > 0 {
+		var total float64
+		for _, p := range s.PSUs {
+			total += p.PowerW
+		}
+		s.PowerW = total
+	} else {
+		s.PowerW = sampleSystemPower()
+	}
+
 	// CPU load — from /proc/stat
 	s.CPULoadPct = sampleCPULoadPct()