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.Tests/Services/CsvValidationServiceTests.cs

@@ -0,0 +1,36 @@
+using SharepointToolbox.Core.Models;
+
+namespace SharepointToolbox.Tests.Services;
+
+public class CsvValidationServiceTests
+{
+    [Fact(Skip = "Implemented in Plan 04-02")]
+    public void ParseAndValidateMembers_ValidCsv_ReturnsValidRows()
+    {
+    }
+
+    [Fact(Skip = "Implemented in Plan 04-02")]
+    public void ParseAndValidateMembers_InvalidEmail_ReturnsErrors()
+    {
+    }
+
+    [Fact(Skip = "Implemented in Plan 04-02")]
+    public void ParseAndValidateSites_TeamWithoutOwner_ReturnsError()
+    {
+    }
+
+    [Fact(Skip = "Implemented in Plan 04-02")]
+    public void ParseAndValidateFolders_ValidCsv_ReturnsValidRows()
+    {
+    }
+
+    [Fact(Skip = "Implemented in Plan 04-02")]
+    public void ParseAndValidate_BomDetection_WorksWithAndWithoutBom()
+    {
+    }
+
+    [Fact(Skip = "Implemented in Plan 04-02")]
+    public void ParseAndValidate_SemicolonDelimiter_DetectedAutomatically()
+    {
+    }
+}