feat(04-01): add Phase 4 models, interfaces, BulkOperationRunner, and test scaffolds

- Install CsvHelper 33.1.0 and Microsoft.Graph 5.74.0 (main + test projects)
- Add 14 core model/enum files (BulkOperationResult, BulkMemberRow, BulkSiteRow, TransferJob, FolderStructureRow, SiteTemplate, SiteTemplateOptions, TemplateLibraryInfo, TemplateFolderInfo, TemplatePermissionGroup, ConflictPolicy, TransferMode, CsvValidationRow)
- Add 6 service interfaces (IFileTransferService, IBulkMemberService, IBulkSiteService, ITemplateService, IFolderStructureService, ICsvValidationService)
- Add BulkOperationRunner with continue-on-error and cancellation support
- Add BulkResultCsvExportService stub (compile-ready)
- Add test scaffolds: BulkOperationRunnerTests (5 passing), BulkResultCsvExportServiceTests (2 passing), CsvValidationServiceTests (6 skipped), TemplateRepositoryTests (4 skipped)

SharepointToolbox/Core/Models/SiteTemplate.cs

@@ -0,0 +1,27 @@
+namespace SharepointToolbox.Core.Models;
+
+public class SiteTemplate
+{
+    public string Id { get; set; } = Guid.NewGuid().ToString();
+    public string Name { get; set; } = string.Empty;
+    public string SourceUrl { get; set; } = string.Empty;
+    public DateTime CapturedAt { get; set; }
+    public string SiteType { get; set; } = string.Empty; // "Team" or "Communication"
+    public SiteTemplateOptions Options { get; set; } = new();
+    public TemplateSettings? Settings { get; set; }
+    public TemplateLogo? Logo { get; set; }
+    public List<TemplateLibraryInfo> Libraries { get; set; } = new();
+    public List<TemplatePermissionGroup> PermissionGroups { get; set; } = new();
+}
+
+public class TemplateSettings
+{
+    public string Title { get; set; } = string.Empty;
+    public string Description { get; set; } = string.Empty;
+    public int Language { get; set; }
+}
+
+public class TemplateLogo
+{
+    public string LogoUrl { get; set; } = string.Empty;
+}