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/Utilities/MathHelper.cs

@@ -0,0 +1,53 @@
+namespace PepLib.Utilities
+{
+    public static class MathHelper
+    {
+        public const double HalfPI = Math.PI * 0.5;
+        public const double TwoPI = Math.PI * 2.0;
+
+        public static double NormalizeAngleRad(double angle)
+        {
+            double r = angle % TwoPI;
+            return r < 0 ? TwoPI + r : r;
+        }
+
+        public static double NormalizeAngleDeg(double angle)
+        {
+            double r = angle % 360.0;
+            return r < 0 ? 360.0 + r : r;
+        }
+
+        public static bool IsAngleBetween(double angle, double a1, double a2, bool reversed = false)
+        {
+            if (reversed)
+                Generic.Swap(ref a1, ref a2);
+
+            var diff = NormalizeAngleRad(a2 - a1);
+
+            // full circle
+            if (a2.IsEqualTo(a1))
+                return true;
+
+            a1 = NormalizeAngleRad(angle - a1);
+            a2 = NormalizeAngleRad(a2 - angle);
+
+            return diff >= a1 - Tolerance.Epsilon ||
+                   diff >= a2 - Tolerance.Epsilon;
+        }
+
+        public static double RoundDownToNearest(double num, double factor)
+        {
+            return factor == 0 ? num : Math.Floor(num / factor) * factor;
+        }
+
+        public static double RoundUpToNearest(double num, double factor)
+        {
+            return factor == 0 ? num : Math.Ceiling(num / factor) * factor;
+        }
+
+        public static double RoundToNearest(double num, double factor)
+        {
+            return factor == 0 ? num : Math.Round(num / factor) * factor;
+        }
+    }
+}