Redesign system power chart as stacked per-PSU area chart

- Add PSUReading struct and PSUs []PSUReading to LiveMetricSample
- Sample per-PSU input watts from IPMI SDR entity 10.x (Power Supply)
- Render stacked filled-area SVG chart (one layer per PSU, cumulative total)
- Fall back to single-line chart on systems with ≤1 PSU in SDR

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

audit/internal/platform/live_metrics.go

@@ -18,11 +18,19 @@ type LiveMetricSample struct {
 	Fans       []FanReading   `json:"fans"`
 	Temps      []TempReading  `json:"temps"`
 	PowerW     float64        `json:"power_w"`
+	PSUs       []PSUReading   `json:"psus,omitempty"`
 	CPULoadPct float64        `json:"cpu_load_pct"`
 	MemLoadPct float64        `json:"mem_load_pct"`
 	GPUs       []GPUMetricRow `json:"gpus"`
 }
 
+// PSUReading is a per-slot power supply input power reading.
+type PSUReading struct {
+	Slot   int     `json:"slot"`
+	Name   string  `json:"name"`
+	PowerW float64 `json:"power_w"`
+}
+
 // TempReading is a named temperature sensor value.
 type TempReading struct {
 	Name    string  `json:"name"`
@@ -57,6 +65,9 @@ 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()
+
 	// CPU load — from /proc/stat
 	s.CPULoadPct = sampleCPULoadPct()
 
@@ -326,3 +337,65 @@ func compactAmbientTempName(chip, name string) string {
 	}
 	return chip + " / " + name
 }
+
+// samplePSUPower reads per-PSU input power via IPMI SDR.
+// It parses `ipmitool sdr elist full` output looking for Power Supply entity
+// sensors (entity ID "10.N") that report a value in Watts.
+// Returns nil when IPMI is unavailable or no PSU Watt sensors exist.
+func samplePSUPower() []PSUReading {
+	out, err := exec.Command("ipmitool", "sdr", "elist", "full").Output()
+	if err != nil || len(out) == 0 {
+		return nil
+	}
+	// map slot → reading (keep highest-watt value per slot in case of duplicates)
+	type entry struct {
+		name   string
+		powerW float64
+	}
+	bySlot := map[int]entry{}
+	for _, line := range strings.Split(string(out), "\n") {
+		parts := strings.Split(line, "|")
+		if len(parts) < 5 {
+			continue
+		}
+		entityID := strings.TrimSpace(parts[3]) // e.g. "10.1"
+		if !strings.HasPrefix(entityID, "10.") {
+			continue // not a Power Supply entity
+		}
+		slotStr := strings.TrimPrefix(entityID, "10.")
+		slot, err := strconv.Atoi(slotStr)
+		if err != nil {
+			continue
+		}
+		valueField := strings.TrimSpace(parts[4]) // e.g. "740.00 Watts"
+		if !strings.Contains(strings.ToLower(valueField), "watts") {
+			continue
+		}
+		valueFields := strings.Fields(valueField)
+		if len(valueFields) < 2 {
+			continue
+		}
+		w, err := strconv.ParseFloat(valueFields[0], 64)
+		if err != nil || w <= 0 {
+			continue
+		}
+		sensorName := strings.TrimSpace(parts[0])
+		if existing, ok := bySlot[slot]; !ok || w > existing.powerW {
+			bySlot[slot] = entry{name: sensorName, powerW: w}
+		}
+	}
+	if len(bySlot) == 0 {
+		return nil
+	}
+	slots := make([]int, 0, len(bySlot))
+	for s := range bySlot {
+		slots = append(slots, s)
+	}
+	sort.Ints(slots)
+	psus := make([]PSUReading, 0, len(slots))
+	for _, s := range slots {
+		e := bySlot[s]
+		psus = append(psus, PSUReading{Slot: s, Name: e.name, PowerW: e.powerW})
+	}
+	return psus
+}