Refactor validate modes, fix benchmark report and IPMI power

- Replace diag level 1-4 dropdown with Validate/Stress radio buttons
- Validate: dcgmi L2, 60s CPU, 256MB/1p memtester, SMART short
- Stress: dcgmi L3 + targeted_stress in Run All, 30min CPU, 1GB/3p memtester, SMART long/NVMe extended
- Parallel GPU mode: spawn single task for all GPUs instead of splitting per model
- Benchmark table: per-GPU columns for sequential runs, server-wide column for parallel
- Benchmark report converted to Markdown with server model, GPU model, version in header; only steady-state charts
- Fix IPMI power parsing in benchmark (was looking for 'Current Power', correct field is 'Instantaneous power reading')

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

audit/internal/webui/server_test.go

@@ -693,8 +693,8 @@ func TestBenchmarkPageRendersSavedResultsTable(t *testing.T) {
 	for _, needle := range []string{
 		`Benchmark Results`,
 		`Composite score by saved benchmark run and GPU.`,
-		`NVIDIA H100 PCIe / GPU 0`,
-		`NVIDIA H100 PCIe / GPU 1`,
+		`GPU #0 — NVIDIA H100 PCIe`,
+		`GPU #1 — NVIDIA H100 PCIe`,
 		`#1`,
 		wantTime,
 		`1176.25`,