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>

PepApi.Core/Controllers/NestsController.cs

@@ -3,8 +3,8 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Options;
 using PepApi.Core.Configuration;
 using PepApi.Core.Models;
-using PepLib;
 using PepLib.Data;
+using PepLib.Models;
 using Plate = PepApi.Core.Models.Plate;
 
 namespace PepApi.Core.Controllers;