refactor(PepLib.Core): reorganize files into logical folder structure

Move 38 files from root directory into organized subfolders:
- Enums/ (7 files): StatusType, ApplicationType, DrawingType, etc.
- Geometry/ (5 files): Vector, Box, Size, Spacing, Node
- Models/ (15 files): Nest, Plate, Part, Program, Report, etc.
- Utilities/ (7 files): MathHelper, Tolerance, ZipHelper, etc.
- Extensions/ (2 files): PartListExtensions, PlateListExtensions
- Interfaces/ (1 file): IMovable

Update namespaces to follow folder hierarchy (e.g., PepLib.Models).
Add GlobalUsings.cs for internal backward compatibility.
Update Codes/ and IO/ files with new using statements.
Update PepApi.Core consumers to reference new namespaces.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PepLib.Core/Models/Loop.cs

@@ -0,0 +1,58 @@
+using PepLib.Codes;
+using PepLib.Enums;
+using PepLib.Geometry;
+
+namespace PepLib.Models
+{
+    public class Loop : Program
+    {
+        public Loop()
+        {
+            Mode = ProgrammingMode.Incremental;
+        }
+
+        public string Name { get; set; }
+
+        public Vector ReferencePoint { get; set; }
+
+        public DateTime LastReferenceDate { get; set; }
+
+        public string DrawingName { get; set; }
+
+        public string DxfPath { get; set; }
+
+        public override void Rotate(double angle)
+        {
+            base.Rotate(angle);
+            ReferencePoint = ReferencePoint.Rotate(angle);
+        }
+
+        public override void Rotate(double angle, Vector origin)
+        {
+            base.Rotate(angle, origin);
+            ReferencePoint = ReferencePoint.Rotate(angle);
+        }
+
+        public object Clone()
+        {
+            var loop = new Loop()
+            {
+                Name = this.Name,
+                ReferencePoint = this.ReferencePoint,
+                LastReferenceDate = this.LastReferenceDate,
+                DrawingName = this.DrawingName,
+                DxfPath = this.DxfPath,
+                Rotation = this.Rotation
+            };
+
+            var codes = new ICode[this.Count];
+
+            for (int i = 0; i < this.Count; ++i)
+                codes[i] = this[i].Clone();
+
+            loop.AddRange(codes);
+
+            return loop;
+        }
+    }
+}