refactor: extract training data collection into OpenNest.Training

Move brute-force data collection, TrainingDatabase, and GPU init from
OpenNest.Console into a dedicated OpenNest.Training project. Replaces
raw Microsoft.Data.Sqlite with EF Core. Console is now a pure nesting
CLI with template support and cleaned-up usage output.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Training/Data/TrainingRun.cs

@@ -0,0 +1,25 @@
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace OpenNest.Training.Data
+{
+    [Table("Runs")]
+    public class TrainingRun
+    {
+        [Key]
+        public long Id { get; set; }
+
+        public long PartId { get; set; }
+        public double SheetWidth { get; set; }
+        public double SheetHeight { get; set; }
+        public double Spacing { get; set; }
+        public int PartCount { get; set; }
+        public double Utilization { get; set; }
+        public long TimeMs { get; set; }
+        public string LayoutData { get; set; }
+        public string FilePath { get; set; }
+
+        [ForeignKey(nameof(PartId))]
+        public TrainingPart Part { get; set; }
+    }
+}