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/platform/gpu_metrics.go

@@ -13,18 +13,19 @@ import (
 
 // GPUMetricRow is one telemetry sample from nvidia-smi during a stress test.
 type GPUMetricRow struct {
-	ElapsedSec float64
-	GPUIndex   int
-	TempC      float64
-	UsagePct   float64
-	PowerW     float64
-	ClockMHz   float64
+	ElapsedSec  float64 `json:"elapsed_sec"`
+	GPUIndex    int     `json:"index"`
+	TempC       float64 `json:"temp_c"`
+	UsagePct    float64 `json:"usage_pct"`
+	MemUsagePct float64 `json:"mem_usage_pct"`
+	PowerW      float64 `json:"power_w"`
+	ClockMHz    float64 `json:"clock_mhz"`
 }
 
 // sampleGPUMetrics runs nvidia-smi once and returns current metrics for each GPU.
 func sampleGPUMetrics(gpuIndices []int) ([]GPUMetricRow, error) {
 	args := []string{
-		"--query-gpu=index,temperature.gpu,utilization.gpu,power.draw,clocks.current.graphics",
+		"--query-gpu=index,temperature.gpu,utilization.gpu,utilization.memory,power.draw,clocks.current.graphics",
 		"--format=csv,noheader,nounits",
 	}
 	if len(gpuIndices) > 0 {
@@ -45,16 +46,17 @@ func sampleGPUMetrics(gpuIndices []int) ([]GPUMetricRow, error) {
 			continue
 		}
 		parts := strings.Split(line, ", ")
-		if len(parts) < 5 {
+		if len(parts) < 6 {
 			continue
 		}
 		idx, _ := strconv.Atoi(strings.TrimSpace(parts[0]))
 		rows = append(rows, GPUMetricRow{
-			GPUIndex: idx,
-			TempC:    parseGPUFloat(parts[1]),
-			UsagePct: parseGPUFloat(parts[2]),
-			PowerW:   parseGPUFloat(parts[3]),
-			ClockMHz: parseGPUFloat(parts[4]),
+			GPUIndex:    idx,
+			TempC:       parseGPUFloat(parts[1]),
+			UsagePct:    parseGPUFloat(parts[2]),
+			MemUsagePct: parseGPUFloat(parts[3]),
+			PowerW:      parseGPUFloat(parts[4]),
+			ClockMHz:    parseGPUFloat(parts[5]),
 		})
 	}
 	return rows, nil