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/NestIndex.cs

@@ -0,0 +1,66 @@
+using PepLib.IO;
+using System.Text;
+
+namespace PepLib.Models
+{
+    public class NestIndex
+    {
+        public string Directory { get; set; }
+
+        public List<NestInfo> Entries;
+
+        public NestIndex()
+        {
+            Entries = new List<NestInfo>();
+        }
+
+        public string GetPath(NestInfo entry)
+        {
+            return Path.Combine(Directory, entry.Name + ".zip");
+        }
+
+        public static NestIndex LoadFromDir(string directory)
+        {
+            var file = Path.Combine(directory, "pepfiles.lfn");
+            return Load(file);
+        }
+
+        public static NestIndex Load(string file)
+        {
+            if (!File.Exists(file))
+                return null;
+
+            var index = new NestIndex() { Directory = Path.GetDirectoryName(file) };
+            var stream = File.Open(file, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
+            var reader = new StreamReader(stream);
+            var buffer = new char[4000];
+
+            while (reader.Read(buffer, 0, buffer.Length) > 0)
+            {
+                var memstream = new MemoryStream(Encoding.ASCII.GetBytes(buffer));
+                var inforeader = new NestInfoReader();
+
+                inforeader.Read(memstream);
+                index.Entries.Add(inforeader.Info);
+            }
+
+            reader.Close();
+
+            return index;
+        }
+
+        public static NestIndex Build(string directory)
+        {
+            var index = new NestIndex() { Directory = directory };
+
+            foreach (var file in System.IO.Directory.GetFiles(directory, "*.zip"))
+            {
+                var reader = new NestInfoReader();
+                reader.Read(file);
+                index.Entries.Add(reader.Info);
+            }
+
+            return index;
+        }
+    }
+}