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/CsvValidationServiceTests.cs

@@ -1,36 +1,128 @@
+using System.IO;
+using System.Text;
 using SharepointToolbox.Core.Models;
+using SharepointToolbox.Services;
 
 namespace SharepointToolbox.Tests.Services;
 
 public class CsvValidationServiceTests
 {
-    [Fact(Skip = "Implemented in Plan 04-02")]
+    private readonly CsvValidationService _service = new();
+
+    private static Stream ToStream(string content)
+    {
+        return new MemoryStream(Encoding.UTF8.GetBytes(content));
+    }
+
+    private static Stream ToStreamWithBom(string content)
+    {
+        var preamble = Encoding.UTF8.GetPreamble();
+        var bytes = Encoding.UTF8.GetBytes(content);
+        var combined = new byte[preamble.Length + bytes.Length];
+        preamble.CopyTo(combined, 0);
+        bytes.CopyTo(combined, preamble.Length);
+        return new MemoryStream(combined);
+    }
+
+    [Fact]
     public void ParseAndValidateMembers_ValidCsv_ReturnsValidRows()
     {
+        var csv = "GroupName,GroupUrl,Email,Role\nTeam A,https://site,user@test.com,Member\n";
+        var rows = _service.ParseAndValidateMembers(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.True(rows[0].IsValid);
+        Assert.Equal("user@test.com", rows[0].Record!.Email);
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
+    [Fact]
     public void ParseAndValidateMembers_InvalidEmail_ReturnsErrors()
     {
+        var csv = "GroupName,GroupUrl,Email,Role\nTeam A,https://site,not-an-email,Member\n";
+        var rows = _service.ParseAndValidateMembers(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.False(rows[0].IsValid);
+        Assert.Contains(rows[0].Errors, e => e.Contains("Invalid email"));
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
+    [Fact]
+    public void ParseAndValidateMembers_MissingGroup_ReturnsError()
+    {
+        var csv = "GroupName,GroupUrl,Email,Role\n,,user@test.com,Member\n";
+        var rows = _service.ParseAndValidateMembers(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.False(rows[0].IsValid);
+        Assert.Contains(rows[0].Errors, e => e.Contains("GroupName or GroupUrl"));
+    }
+
+    [Fact]
     public void ParseAndValidateSites_TeamWithoutOwner_ReturnsError()
     {
+        var csv = "Name;Alias;Type;Template;Owners;Members\nSite A;site-a;Team;;;\n";
+        var rows = _service.ParseAndValidateSites(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.False(rows[0].IsValid);
+        Assert.Contains(rows[0].Errors, e => e.Contains("owner"));
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
+    [Fact]
+    public void ParseAndValidateSites_ValidTeam_ReturnsValid()
+    {
+        var csv = "Name;Alias;Type;Template;Owners;Members\nSite A;site-a;Team;;admin@test.com;user@test.com\n";
+        var rows = _service.ParseAndValidateSites(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.True(rows[0].IsValid);
+        Assert.Equal("Site A", rows[0].Record!.Name);
+    }
+
+    [Fact]
     public void ParseAndValidateFolders_ValidCsv_ReturnsValidRows()
     {
+        var csv = "Level1;Level2;Level3;Level4\nAdmin;HR;;\n";
+        var rows = _service.ParseAndValidateFolders(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.True(rows[0].IsValid);
+        Assert.Equal("Admin", rows[0].Record!.Level1);
+        Assert.Equal("HR", rows[0].Record!.Level2);
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
+    [Fact]
+    public void ParseAndValidateFolders_MissingLevel1_ReturnsError()
+    {
+        var csv = "Level1;Level2;Level3;Level4\n;SubFolder;;\n";
+        var rows = _service.ParseAndValidateFolders(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.False(rows[0].IsValid);
+        Assert.Contains(rows[0].Errors, e => e.Contains("Level1"));
+    }
+
+    [Fact]
     public void ParseAndValidate_BomDetection_WorksWithAndWithoutBom()
     {
+        var csv = "GroupName,GroupUrl,Email,Role\nTeam A,https://site,user@test.com,Member\n";
+        var rowsNoBom = _service.ParseAndValidateMembers(ToStream(csv));
+        var rowsWithBom = _service.ParseAndValidateMembers(ToStreamWithBom(csv));
+
+        Assert.Single(rowsNoBom);
+        Assert.Single(rowsWithBom);
+        Assert.True(rowsNoBom[0].IsValid);
+        Assert.True(rowsWithBom[0].IsValid);
     }
 
-    [Fact(Skip = "Implemented in Plan 04-02")]
+    [Fact]
     public void ParseAndValidate_SemicolonDelimiter_DetectedAutomatically()
     {
+        var csv = "Name;Alias;Type;Template;Owners;Members\nSite A;site-a;Communication;;;;\n";
+        var rows = _service.ParseAndValidateSites(ToStream(csv));
+
+        Assert.Single(rows);
+        Assert.Equal("Site A", rows[0].Record!.Name);
+        Assert.Equal("Communication", rows[0].Record!.Type);
     }
 }