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/ApplicationDbContext.cs

@@ -234,6 +234,8 @@ public class ApplicationDbContext : DbContext
             entity.Property(e => e.Customer).HasMaxLength(100);
             entity.Property(e => e.CreatedAt).HasDefaultValueSql("GETUTCDATE()");
 
+            entity.Property(e => e.OptimizationResultJson).HasColumnType("nvarchar(max)");
+
             entity.HasIndex(e => e.JobNumber).IsUnique();
 
             entity.HasOne(e => e.CuttingTool)