Add scalability/ramp-up labeling, ServerPower penalty in scoring, and report improvements

- Add RampStep/RampTotal/RampRunID to NvidiaBenchmarkOptions, taskParams, and
  NvidiaBenchmarkResult so ramp-up steps can be correlated across result.json files
- Add ScalabilityScore field to NvidiaBenchmarkResult (placeholder; computed externally
  by comparing ramp-up step results sharing the same ramp_run_id)
- Propagate ramp fields through api.go (generates shared ramp_run_id at spawn time),
  tasks.go handler, and benchmark.go result population
- Apply ServerPower penalty to CompositeScore when IPMI reporting_ratio < 0.75:
  factor = ratio/0.75, applied per-GPU with a note explaining the reduction
- Add finding when server power delta exceeds GPU-reported sum by >25% (non-GPU draw)
- Report header now shows ramp step N/M and run ID instead of "parallel" when in ramp mode;
  shows scalability_score when non-zero

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

audit/internal/platform/benchmark_report.go

@@ -60,9 +60,17 @@ func renderBenchmarkReportWithCharts(result NvidiaBenchmarkResult, charts []benc
 	fmt.Fprintf(&b, "**Profile:** %s  \n", result.BenchmarkProfile)
 	fmt.Fprintf(&b, "**App version:** %s  \n", result.BenchmarkVersion)
 	fmt.Fprintf(&b, "**Generated:** %s  \n", result.GeneratedAt.Format("2006-01-02 15:04:05 UTC"))
-	if result.ParallelGPUs {
+	if result.RampStep > 0 && result.RampTotal > 0 {
+		fmt.Fprintf(&b, "**Ramp-up step:** %d of %d  \n", result.RampStep, result.RampTotal)
+		if result.RampRunID != "" {
+			fmt.Fprintf(&b, "**Ramp-up run ID:** %s  \n", result.RampRunID)
+		}
+	} else if result.ParallelGPUs {
 		fmt.Fprintf(&b, "**Mode:** parallel (all GPUs simultaneously)  \n")
 	}
+	if result.ScalabilityScore > 0 {
+		fmt.Fprintf(&b, "**Scalability score:** %.1f%%  \n", result.ScalabilityScore)
+	}
 	fmt.Fprintf(&b, "**Overall status:** %s  \n", result.OverallStatus)
 	b.WriteString("\n")