refactor(webui): redesign Burn tab and fix gpu-burn memory defaults

- Burn tab: replace 6 flat cards with 3 grouped cards (GPU Stress,
  Compute Stress, Platform Thermal Cycling) + global Burn Profile
- Run All button at top enqueues all enabled tests across all cards
- GPU Stress: tool checkboxes enabled/disabled via new /api/gpu/tools
  endpoint based on driver status (/dev/nvidia0, /dev/kfd)
- Compute Stress: checkboxes for cpu/memory-stress/stressapptest
- Platform Thermal Cycling: component checkboxes (cpu/nvidia/amd)
  with platform_components param wired through to PlatformStressOptions
- bee-gpu-burn: default size-mb changed from 64 to 0 (auto); script
  now queries nvidia-smi memory.total per GPU and uses 95% of it
- platform_stress: removed hardcoded --size-mb 64; respects Components
  field to selectively run CPU and/or GPU load goroutines

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

audit/internal/webui/server.go

@@ -255,8 +255,9 @@ func NewHandler(opts HandlerOptions) http.Handler {
 	mux.HandleFunc("GET /api/display/resolutions", h.handleAPIDisplayResolutions)
 	mux.HandleFunc("POST /api/display/set", h.handleAPIDisplaySet)
 
-	// GPU presence
+	// GPU presence / tools
 	mux.HandleFunc("GET /api/gpu/presence", h.handleAPIGPUPresence)
+	mux.HandleFunc("GET /api/gpu/tools", h.handleAPIGPUTools)
 
 	// System
 	mux.HandleFunc("GET /api/system/ram-status", h.handleAPIRAMStatus)
@@ -516,6 +517,7 @@ func (h *handler) handleMetricsChartSVG(w http.ResponseWriter, r *http.Request)
 	case path == "server-power":
 		title = "System Power"
 		vPower, l := h.ringPower.snapshot()
+		vPower = normalizePowerSeries(vPower)
 		labels = l
 		datasets = [][]float64{vPower}
 		names = []string{"Power W"}
@@ -728,9 +730,11 @@ func chartDataFromSamples(path string, samples []platform.LiveMetricSample) ([][
 		for i, s := range samples {
 			power[i] = s.PowerW
 		}
+		power = normalizePowerSeries(power)
 		datasets = [][]float64{power}
 		names = []string{"Power W"}
-		yMin, yMax = autoBounds120(power)
+		yMin = floatPtr(0)
+		yMax = autoMax120(power)
 
 	case path == "server-fans":
 		title = "Fan RPM"
@@ -928,6 +932,27 @@ func coalesceDataset(ds []float64, n int) []float64 {
 	return make([]float64, n)
 }
 
+func normalizePowerSeries(ds []float64) []float64 {
+	if len(ds) == 0 {
+		return nil
+	}
+	out := make([]float64, len(ds))
+	copy(out, ds)
+	last := 0.0
+	haveLast := false
+	for i, v := range out {
+		if v > 0 {
+			last = v
+			haveLast = true
+			continue
+		}
+		if haveLast {
+			out[i] = last
+		}
+	}
+	return out
+}
+
 // floatPtr returns a pointer to a float64 value.
 func floatPtr(v float64) *float64 { return &v }