Redesign power and performance benchmarks with new methodology

Power/Thermal Fit: cumulative fixed-limit ramp where each GPU's stable TDP
is found under real multi-GPU thermal load (all prior GPUs running at their
fixed limits). PlatformMaxTDPW = sum of stable limits across all GPUs.
Remove PlatformPowerScore from power test.

Performance Benchmark: remove pre-benchmark power calibration entirely.
After N single-card runs, execute k=2..N parallel ramp-up steps and compute
PlatformPowerScore = mean compute scalability vs best single-card TOPS.
PowerSustainScore falls back to Steady.AvgPowerW when calibration absent.

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

audit/internal/platform/benchmark_report.go

@@ -61,6 +61,9 @@ func renderBenchmarkReportWithCharts(result NvidiaBenchmarkResult) string {
 	if result.ScalabilityScore > 0 {
 		fmt.Fprintf(&b, "**Scalability score:** %.1f%%  \n", result.ScalabilityScore)
 	}
+	if result.PlatformPowerScore > 0 {
+		fmt.Fprintf(&b, "**Platform power score:** %.1f%%  \n", result.PlatformPowerScore)
+	}
 	fmt.Fprintf(&b, "**Overall status:** %s  \n", result.OverallStatus)
 	b.WriteString("\n")
 
@@ -329,6 +332,19 @@ func renderBenchmarkReportWithCharts(result NvidiaBenchmarkResult) string {
 		}
 	}
 
+	// ── Platform Scalability ──────────────────────────────────────────────────
+	if len(result.PerformanceRampSteps) > 0 {
+		b.WriteString("## Platform Scalability (Performance Ramp)\n\n")
+		fmt.Fprintf(&b, "**Platform power score:** %.1f%%  \n\n", result.PlatformPowerScore)
+		b.WriteString("| k GPUs | GPU Indices | Total Synthetic TOPS | Scalability |\n")
+		b.WriteString("|--------|-------------|----------------------|-------------|\n")
+		for _, step := range result.PerformanceRampSteps {
+			fmt.Fprintf(&b, "| %d | %s | %.2f | %.1f%% |\n",
+				step.StepIndex, joinIndexList(step.GPUIndices), step.TotalSyntheticTOPS, step.ScalabilityPct)
+		}
+		b.WriteString("\n")
+	}
+
 	// ── Raw files ─────────────────────────────────────────────────────────────
 	b.WriteString("## Raw Files\n\n")
 	b.WriteString("- `result.json`\n- `report.md`\n- `summary.txt`\n- `verbose.log`\n")