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/CsvValidationRow.cs

@@ -0,0 +1,25 @@
+namespace SharepointToolbox.Core.Models;
+
+public class CsvValidationRow<T>
+{
+    public T? Record { get; }
+    public bool IsValid => Errors.Count == 0;
+    public List<string> Errors { get; }
+    public string? RawRecord { get; }
+
+    public CsvValidationRow(T record, List<string> errors)
+    {
+        Record = record;
+        Errors = errors;
+    }
+
+    private CsvValidationRow(string rawRecord, string parseError)
+    {
+        Record = default;
+        RawRecord = rawRecord;
+        Errors = new List<string> { parseError };
+    }
+
+    public static CsvValidationRow<T> ParseError(string? rawRecord, string error)
+        => new(rawRecord ?? string.Empty, error);
+}