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/webui/api.go

@@ -594,6 +594,7 @@ func (h *handler) handleAPIBenchmarkNvidiaRun(w http.ResponseWriter, r *http.Req
 			rampUp = false
 		} else {
 			now := time.Now()
+			rampRunID := fmt.Sprintf("ramp-%s", now.UTC().Format("20060102-150405"))
 			var allTasks []*Task
 			for step := 1; step <= len(resolved); step++ {
 				subset := resolved[:step]
@@ -611,6 +612,9 @@ func (h *handler) handleAPIBenchmarkNvidiaRun(w http.ResponseWriter, r *http.Req
 						BenchmarkProfile: body.Profile,
 						RunNCCL:          runNCCL && step == len(resolved),
 						ParallelGPUs:     true,
+						RampStep:         step,
+						RampTotal:        len(resolved),
+						RampRunID:        rampRunID,
 						DisplayName:      stepName,
 					},
 				}