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/platform/nvidia_stress.go

@@ -95,9 +95,7 @@ func normalizeNvidiaStressOptions(opts *NvidiaStressOptions) {
 	if opts.DurationSec <= 0 {
 		opts.DurationSec = 300
 	}
-	if opts.SizeMB <= 0 {
-		opts.SizeMB = 64
-	}
+	// SizeMB=0 means "auto" — bee-gpu-burn will query per-GPU memory at runtime.
 	switch strings.TrimSpace(strings.ToLower(opts.Loader)) {
 	case "", NvidiaStressLoaderBuiltin:
 		opts.Loader = NvidiaStressLoaderBuiltin