feat(04-02): implement CsvValidationService and TemplateRepository with tests

- CsvValidationService: CsvHelper-based parsing with DetectDelimiter, BOM detection,
  per-row validation for BulkMemberRow/BulkSiteRow/FolderStructureRow
- TemplateRepository: atomic JSON write (tmp + File.Move) with SemaphoreSlim,
  supports GetAll/GetById/Save/Delete/Rename operations
- CsvValidationServiceTests: 9 passing tests (email validation, delimiter detection,
  BOM handling, folder/site/member validation)
- TemplateRepositoryTests: 6 passing tests (round-trip, GetAll, delete, rename,
  empty directory, non-existent id)
- All previously-skipped scaffold tests now active and passing (15 total)

SharepointToolbox.Tests/Services/TemplateRepositoryTests.cs

@@ -1,26 +1,107 @@
+using System.IO;
 using SharepointToolbox.Core.Models;
+using SharepointToolbox.Infrastructure.Persistence;
 
 namespace SharepointToolbox.Tests.Services;
 
-public class TemplateRepositoryTests
+public class TemplateRepositoryTests : IDisposable
 {
-    [Fact(Skip = "Implemented in Plan 04-02")]
-    public void SaveAndLoad_RoundTrips_Correctly()
+    private readonly string _tempDir;
+    private readonly TemplateRepository _repo;
+
+    public TemplateRepositoryTests()
     {
+        _tempDir = Path.Combine(Path.GetTempPath(), $"sptoolbox_test_{Guid.NewGuid():N}");
+        _repo = new TemplateRepository(_tempDir);
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
-    public void GetAll_ReturnsAllSavedTemplates()
+    public void Dispose()
     {
+        if (Directory.Exists(_tempDir))
+            Directory.Delete(_tempDir, true);
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
-    public void Delete_RemovesTemplate()
+    private static SiteTemplate CreateTestTemplate(string name = "Test Template")
     {
+        return new SiteTemplate
+        {
+            Id = Guid.NewGuid().ToString(),
+            Name = name,
+            SourceUrl = "https://contoso.sharepoint.com/sites/test",
+            CapturedAt = DateTime.UtcNow,
+            SiteType = "Team",
+            Options = new SiteTemplateOptions(),
+            Settings = new TemplateSettings { Title = "Test", Description = "Desc", Language = 1033 },
+            Libraries = new List<TemplateLibraryInfo>
+            {
+                new() { Name = "Documents", BaseType = "DocumentLibrary", BaseTemplate = 101 }
+            },
+        };
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
-    public void Rename_UpdatesTemplateName()
+    [Fact]
+    public async Task SaveAndLoad_RoundTrips_Correctly()
     {
+        var template = CreateTestTemplate();
+        await _repo.SaveAsync(template);
+
+        var loaded = await _repo.GetByIdAsync(template.Id);
+
+        Assert.NotNull(loaded);
+        Assert.Equal(template.Name, loaded!.Name);
+        Assert.Equal(template.SiteType, loaded.SiteType);
+        Assert.Equal(template.SourceUrl, loaded.SourceUrl);
+        Assert.Single(loaded.Libraries);
+        Assert.Equal("Documents", loaded.Libraries[0].Name);
+    }
+
+    [Fact]
+    public async Task GetAll_ReturnsAllSavedTemplates()
+    {
+        await _repo.SaveAsync(CreateTestTemplate("Template A"));
+        await _repo.SaveAsync(CreateTestTemplate("Template B"));
+        await _repo.SaveAsync(CreateTestTemplate("Template C"));
+
+        var all = await _repo.GetAllAsync();
+
+        Assert.Equal(3, all.Count);
+    }
+
+    [Fact]
+    public async Task Delete_RemovesTemplate()
+    {
+        var template = CreateTestTemplate();
+        await _repo.SaveAsync(template);
+        Assert.NotNull(await _repo.GetByIdAsync(template.Id));
+
+        await _repo.DeleteAsync(template.Id);
+
+        Assert.Null(await _repo.GetByIdAsync(template.Id));
+    }
+
+    [Fact]
+    public async Task Rename_UpdatesTemplateName()
+    {
+        var template = CreateTestTemplate("Old Name");
+        await _repo.SaveAsync(template);
+
+        await _repo.RenameAsync(template.Id, "New Name");
+
+        var loaded = await _repo.GetByIdAsync(template.Id);
+        Assert.Equal("New Name", loaded!.Name);
+    }
+
+    [Fact]
+    public async Task GetAll_EmptyDirectory_ReturnsEmptyList()
+    {
+        var all = await _repo.GetAllAsync();
+        Assert.Empty(all);
+    }
+
+    [Fact]
+    public async Task GetById_NonExistent_ReturnsNull()
+    {
+        var result = await _repo.GetByIdAsync("nonexistent-id");
+        Assert.Null(result);
     }
 }