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/TrainingDatabase.cs

@@ -0,0 +1,131 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using Microsoft.EntityFrameworkCore;
+using OpenNest.Engine.ML;
+using OpenNest.IO;
+using OpenNest.Training.Data;
+
+namespace OpenNest.Training
+{
+    public class TrainingDatabase : IDisposable
+    {
+        private readonly TrainingDbContext _db;
+
+        public TrainingDatabase(string dbPath)
+        {
+            if (!dbPath.EndsWith(".db", StringComparison.OrdinalIgnoreCase))
+                dbPath += ".db";
+
+            _db = new TrainingDbContext(dbPath);
+            _db.Database.EnsureCreated();
+        }
+
+        public long GetOrAddPart(string fileName, PartFeatures features, string geometryData)
+        {
+            var existing = _db.Parts.FirstOrDefault(p => p.FileName == fileName);
+            if (existing != null) return existing.Id;
+
+            var part = new TrainingPart
+            {
+                FileName = fileName,
+                Area = features.Area,
+                Convexity = features.Convexity,
+                AspectRatio = features.AspectRatio,
+                BBFill = features.BoundingBoxFill,
+                Circularity = features.Circularity,
+                PerimeterToAreaRatio = features.PerimeterToAreaRatio,
+                VertexCount = features.VertexCount,
+                Bitmask = features.Bitmask,
+                GeometryData = geometryData
+            };
+
+            _db.Parts.Add(part);
+            _db.SaveChanges();
+            return part.Id;
+        }
+
+        public bool HasRun(string fileName, double sheetWidth, double sheetHeight, double spacing)
+        {
+            return _db.Runs.Any(r =>
+                r.Part.FileName == fileName &&
+                r.SheetWidth == sheetWidth &&
+                r.SheetHeight == sheetHeight &&
+                r.Spacing == spacing);
+        }
+
+        public int RunCount(string fileName)
+        {
+            return _db.Runs.Count(r => r.Part.FileName == fileName);
+        }
+
+        public void AddRun(long partId, double w, double h, double s, BruteForceResult result, string filePath)
+        {
+            var run = new TrainingRun
+            {
+                PartId = partId,
+                SheetWidth = w,
+                SheetHeight = h,
+                Spacing = s,
+                PartCount = result.PartCount,
+                Utilization = result.Utilization,
+                TimeMs = result.TimeMs,
+                LayoutData = result.LayoutData ?? "",
+                FilePath = filePath ?? ""
+            };
+
+            _db.Runs.Add(run);
+            _db.SaveChanges();
+        }
+
+        public int BackfillPerimeterToAreaRatio()
+        {
+            var partsToFix = _db.Parts
+                .Where(p => p.PerimeterToAreaRatio == 0)
+                .Select(p => new { p.Id, p.GeometryData })
+                .ToList();
+
+            if (partsToFix.Count == 0) return 0;
+
+            var updated = 0;
+            foreach (var item in partsToFix)
+            {
+                try
+                {
+                    var stream = new MemoryStream(Encoding.UTF8.GetBytes(item.GeometryData));
+                    var programReader = new ProgramReader(stream);
+                    var program = programReader.Read();
+
+                    var drawing = new Drawing("backfill") { Program = program };
+                    drawing.UpdateArea();
+
+                    var features = FeatureExtractor.Extract(drawing);
+                    if (features == null) continue;
+
+                    var part = _db.Parts.Find(item.Id);
+                    part.PerimeterToAreaRatio = features.PerimeterToAreaRatio;
+                    _db.SaveChanges();
+                    updated++;
+                }
+                catch
+                {
+                    // Skip parts that fail to reconstruct.
+                }
+            }
+
+            return updated;
+        }
+
+        public void SaveChanges()
+        {
+            _db.SaveChanges();
+        }
+
+        public void Dispose()
+        {
+            _db?.Dispose();
+        }
+    }
+}