feat: Add optimization result persistence to Job entity

Add OptimizationResultJson and OptimizedAt columns to Job table.
JobService now saves/clears optimization results and auto-clears
stale results when parts, stock, or cutting tool change.

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

CutList.Web/Data/Entities/Job.cs

@@ -11,6 +11,8 @@ public class Job
     public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
     public DateTime? UpdatedAt { get; set; }
     public DateTime? LockedAt { get; set; }
+    public string? OptimizationResultJson { get; set; }
+    public DateTime? OptimizedAt { get; set; }
 
     public bool IsLocked => LockedAt.HasValue;