fix(benchmark): rank by sheet cost so engines can't game the score

The benchmark is about to be used as the objective for LLM-designed
engines, and several gaps would have rewarded the wrong behavior:

- Ranking was utilization-first, so dropping awkward parts raised the
  score. Rank valid > fully placed > cost > plates, where cost is
  salvage-credited sheet area plus a largest-sheet penalty per unplaced
  part; placing a part is never scored worse than omitting it.
- Salvage rate was ignored in scoring; cost now uses EstimateNetArea,
  recomputed from job geometry rather than trusted from the engine.
- Rotation constraints were never validated. Add RotationPolicy.Allows
  (shared with NestJobPlacementValidator) and check every placement.
- Returned sheets were trusted, so an engine could loosen spacing or
  invent a size. Sheets must now match offered stock.
- Part-in-part placements were flagged as overlaps; spacing now accounts
  for cutouts, with an X-sorted sweep to prune distant pairs.
- Summary averaged per-job percentages; it now sums areas and cost.
- --spacing and sheet sizes parsed with the current culture.
- Warn when .nest jobs offer only their original sheet sizes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Benchmark/BenchmarkRunner.cs

@@ -100,11 +100,21 @@ namespace OpenNest.Benchmark
                 );
 
                 var validation = NestValidator.Validate(plateRuns, requirements);
+                NestValidator.ValidateAgainstJob(
+                    nestJob,
+                    jobResult,
+                    job.Requests.ToDictionary(r => r.Drawing.Id.ToString(), r => r.Drawing.Name),
+                    validation
+                );
                 var totalPlaced = plateRuns.Sum(pr => pr.Parts.Count);
                 var placedArea = validation.Valid
                     ? plateRuns.Sum(pr => pr.Parts.Sum(p => p.BaseDrawing.Area))
                     : 0;
                 var plateArea = plateRuns.Sum(pr => pr.Plate.Area());
+                // Salvage credit is recomputed from the job's own geometry, never taken from the engine.
+                var netSheetArea = validation.Valid
+                    ? jobResult.Plates.Sum(p => StockLadderNestingEngine.EstimateNetArea(nestJob, p))
+                    : 0;
 
                 var sizeBreakdown = plateRuns
                     .GroupBy(pr => pr.Plate.Size.ToString(1))
@@ -157,9 +167,7 @@ namespace OpenNest.Benchmark
                         PlacedArea = placedArea,
                         SalvageRate = salvageRate,
                         MinimumSalvageDimension = minimumSalvageDimension,
-                        EstimatedNetArea = jobResult.Plates.Sum(p =>
-                            StockLadderNestingEngine.EstimateNetArea(nestJob, p)
-                        ),
+                        EstimatedNetArea = netSheetArea,
                         Fulfillment = jobResult.Fulfillment,
                         StockUsage = jobResult.StockUsage,
                         Plates = jobResult.Plates,
@@ -185,6 +193,8 @@ namespace OpenNest.Benchmark
                     PartsRequested = requested,
                     PlacedArea = placedArea,
                     PlateArea = plateArea,
+                    NetSheetArea = netSheetArea,
+                    UnplacedPartPenalty = job.UnplacedPartPenalty,
                     PlatesUsed = plateRuns.Count,
                     SizeBreakdown = sizeBreakdown,
                     ElapsedMs = sw.ElapsedMilliseconds,
@@ -199,6 +209,7 @@ namespace OpenNest.Benchmark
                     JobName = job.Name,
                     Valid = false,
                     PartsRequested = requested,
+                    UnplacedPartPenalty = job.UnplacedPartPenalty,
                     ElapsedMs = sw.ElapsedMilliseconds,
                     Error = $"Timed out after {SolveTimeout.TotalMinutes:F0} minute(s)",
                 };
@@ -212,6 +223,7 @@ namespace OpenNest.Benchmark
                     JobName = job.Name,
                     Valid = false,
                     PartsRequested = requested,
+                    UnplacedPartPenalty = job.UnplacedPartPenalty,
                     ElapsedMs = sw.ElapsedMilliseconds,
                     Error = $"{ex.GetType().Name}: {ex.Message}",
                 };