Detect PSU faults during perf and power benchmarks

Snapshot IPMI "Power Supply" sensor states before and after each benchmark
run. Compare before/after to surface only *new* anomalies (pre-existing faults
are excluded). Results land in NvidiaBenchmarkResult.PSUIssues and
NvidiaPowerBenchResult.PSUIssues (JSON: psu_issues) and are printed in the
text benchmark report under a "PSU Issues" section.

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

audit/internal/platform/benchmark_report.go

@@ -383,6 +383,16 @@ func renderBenchmarkReportWithCharts(result NvidiaBenchmarkResult) string {
 		}
 	}
 
+	// ── PSU Issues ────────────────────────────────────────────────────────────
+	if len(result.PSUIssues) > 0 {
+		b.WriteString("## PSU Issues\n\n")
+		b.WriteString("The following power supply anomalies were detected during the benchmark:\n\n")
+		for _, issue := range result.PSUIssues {
+			fmt.Fprintf(&b, "- ⛔ %s\n", issue)
+		}
+		b.WriteString("\n")
+	}
+
 	// ── Cooling ───────────────────────────────────────────────────────────────
 	if cooling := result.Cooling; cooling != nil {
 		b.WriteString("## Cooling\n\n")