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/TrainingPart.cs

@@ -0,0 +1,28 @@
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace OpenNest.Training.Data
+{
+    [Table("Parts")]
+    public class TrainingPart
+    {
+        [Key]
+        public long Id { get; set; }
+
+        [MaxLength(260)]
+        public string FileName { get; set; }
+
+        public double Area { get; set; }
+        public double Convexity { get; set; }
+        public double AspectRatio { get; set; }
+        public double BBFill { get; set; }
+        public double Circularity { get; set; }
+        public double PerimeterToAreaRatio { get; set; }
+        public int VertexCount { get; set; }
+        public byte[] Bitmask { get; set; }
+        public string GeometryData { get; set; }
+
+        public List<TrainingRun> Runs { get; set; } = new();
+    }
+}