feat(metrics): single chart engine + full-width stacked layout

- One engine: go-analyze/charts (grafana theme) for all live metrics
- Server chart: CPU temp, CPU load%, mem load%, power W, fan RPMs
- GPU charts: temp, load%, mem%, power W — one card per GPU, added dynamically
- Charts 1400x280px SVG, rendered at width:100% in single-column layout
- Add CPU load (from /proc/stat) and mem load (from /proc/meminfo) to LiveMetricSample
- Add GPU mem utilization to GPUMetricRow (nvidia-smi utilization.memory)
- Document charting architecture in bible-local/architecture/charting.md

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

audit/internal/webui/server.go

@@ -62,15 +62,27 @@ func (r *metricsRing) snapshot() ([]float64, []string) {
 	return v, l
 }
 
+// gpuRings holds per-GPU ring buffers.
+type gpuRings struct {
+	Temp    *metricsRing
+	Util    *metricsRing
+	MemUtil *metricsRing
+	Power   *metricsRing
+}
+
 // handler is the HTTP handler for the web UI.
 type handler struct {
-	opts       HandlerOptions
-	mux        *http.ServeMux
+	opts        HandlerOptions
+	mux         *http.ServeMux
+	// server rings
 	ringCPUTemp *metricsRing
+	ringCPULoad *metricsRing
+	ringMemLoad *metricsRing
 	ringPower   *metricsRing
 	ringFans    []*metricsRing
-	ringGPUTemp []*metricsRing
-	ringGPUUtil []*metricsRing
+	fanNames    []string
+	// per-GPU rings (index = GPU index)
+	gpuRings    []*gpuRings
 	ringsMu     sync.Mutex
 }
 
@@ -89,6 +101,8 @@ func NewHandler(opts HandlerOptions) http.Handler {
 	h := &handler{
 		opts:        opts,
 		ringCPUTemp: newMetricsRing(120),
+		ringCPULoad: newMetricsRing(120),
+		ringMemLoad: newMetricsRing(120),
 		ringPower:   newMetricsRing(120),
 	}
 	mux := http.NewServeMux()
@@ -244,48 +258,88 @@ func (h *handler) handleViewer(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *handler) handleMetricsChartSVG(w http.ResponseWriter, r *http.Request) {
-	name := strings.TrimPrefix(r.URL.Path, "/api/metrics/chart/")
-	name = strings.TrimSuffix(name, ".svg")
+	path := strings.TrimPrefix(r.URL.Path, "/api/metrics/chart/")
+	path = strings.TrimSuffix(path, ".svg")
+
+	var datasets [][]float64
+	var names []string
+	var labels []string
+	var title string
+
+	switch {
+	case path == "server":
+		title = "Server"
+		vCPUTemp, l := h.ringCPUTemp.snapshot()
+		vCPULoad, _ := h.ringCPULoad.snapshot()
+		vMemLoad, _ := h.ringMemLoad.snapshot()
+		vPower, _ := h.ringPower.snapshot()
+		labels = l
+		datasets = [][]float64{vCPUTemp, vCPULoad, vMemLoad, vPower}
+		names = []string{"CPU Temp °C", "CPU Load %", "Mem Load %", "Power W"}
+
+		h.ringsMu.Lock()
+		for i, fr := range h.ringFans {
+			fv, _ := fr.snapshot()
+			datasets = append(datasets, fv)
+			name := "Fan"
+			if i < len(h.fanNames) {
+				name = h.fanNames[i]
+			}
+			names = append(names, name+" RPM")
+		}
+		h.ringsMu.Unlock()
+
+	case strings.HasPrefix(path, "gpu/"):
+		idxStr := strings.TrimPrefix(path, "gpu/")
+		idx := 0
+		fmt.Sscanf(idxStr, "%d", &idx)
+		h.ringsMu.Lock()
+		var gr *gpuRings
+		if idx < len(h.gpuRings) {
+			gr = h.gpuRings[idx]
+		}
+		h.ringsMu.Unlock()
+		if gr == nil {
+			http.NotFound(w, r)
+			return
+		}
+		vTemp, l := gr.Temp.snapshot()
+		vUtil, _ := gr.Util.snapshot()
+		vMemUtil, _ := gr.MemUtil.snapshot()
+		vPower, _ := gr.Power.snapshot()
+		labels = l
+		title = fmt.Sprintf("GPU %d", idx)
+		datasets = [][]float64{vTemp, vUtil, vMemUtil, vPower}
+		names = []string{"Temp °C", "Load %", "Mem %", "Power W"}
 
-	var ring *metricsRing
-	var title, unit string
-	switch name {
-	case "cpu-temp":
-		ring, title, unit = h.ringCPUTemp, "CPU Temperature", "°C"
-	case "power":
-		ring, title, unit = h.ringPower, "System Power", "W"
 	default:
 		http.NotFound(w, r)
 		return
 	}
 
-	vals, labels := ring.snapshot()
-	if len(vals) == 0 {
-		vals = []float64{0}
+	// Ensure all datasets same length as labels
+	n := len(labels)
+	if n == 0 {
+		n = 1
 		labels = []string{""}
 	}
-
-	// Sparse x-axis labels
-	sparse := make([]string, len(labels))
-	step := len(labels) / 6
-	if step < 1 {
-		step = 1
-	}
-	for i := range labels {
-		if i%step == 0 {
-			sparse[i] = labels[i]
+	for i := range datasets {
+		if len(datasets[i]) == 0 {
+			datasets[i] = make([]float64, n)
 		}
 	}
 
-	opt := gocharts.NewLineChartOptionWithData([][]float64{vals})
-	opt.Title = gocharts.TitleOption{Text: title + " (" + unit + ")"}
+	sparse := sparseLabels(labels, 6)
+
+	opt := gocharts.NewLineChartOptionWithData(datasets)
+	opt.Title = gocharts.TitleOption{Text: title}
 	opt.XAxis.Labels = sparse
-	opt.Legend = gocharts.LegendOption{Show: gocharts.Ptr(false)}
+	opt.Legend = gocharts.LegendOption{SeriesNames: names}
 
 	p := gocharts.NewPainter(gocharts.PainterOptions{
 		OutputFormat: gocharts.ChartOutputSVG,
-		Width:        600,
-		Height:       180,
+		Width:        1400,
+		Height:       280,
 	}, gocharts.PainterThemeOption(gocharts.GetTheme("grafana")))
 	if err := p.LineChart(opt); err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
@@ -301,6 +355,27 @@ func (h *handler) handleMetricsChartSVG(w http.ResponseWriter, r *http.Request)
 	_, _ = w.Write(buf)
 }
 
+func safeIdx(s []float64, i int) float64 {
+	if i < len(s) {
+		return s[i]
+	}
+	return 0
+}
+
+func sparseLabels(labels []string, n int) []string {
+	out := make([]string, len(labels))
+	step := len(labels) / n
+	if step < 1 {
+		step = 1
+	}
+	for i, l := range labels {
+		if i%step == 0 {
+			out[i] = l
+		}
+	}
+	return out
+}
+
 // ── Page handler ─────────────────────────────────────────────────────────────
 
 func (h *handler) handlePage(w http.ResponseWriter, r *http.Request) {