feat(10-01): create logo models, BrandingRepository, and repository tests

- Add LogoData record with Base64 and MimeType init properties
- Add BrandingSettings class with nullable MspLogo property
- Extend TenantProfile with nullable ClientLogo property (additive)
- Add BrandingRepository mirroring SettingsRepository pattern (write-then-replace)
- Add BrandingRepositoryTests: 5 tests covering load defaults, round-trip, dir creation, and TenantProfile serialization

SharepointToolbox.Tests/Services/BrandingRepositoryTests.cs

@@ -0,0 +1,130 @@
+using System.IO;
+using System.Text;
+using System.Text.Json;
+using SharepointToolbox.Core.Models;
+using SharepointToolbox.Infrastructure.Persistence;
+
+namespace SharepointToolbox.Tests.Services;
+
+[Trait("Category", "Unit")]
+public class BrandingRepositoryTests : IDisposable
+{
+    private readonly string _tempFile;
+
+    public BrandingRepositoryTests()
+    {
+        _tempFile = Path.GetTempFileName();
+        File.Delete(_tempFile);
+    }
+
+    public void Dispose()
+    {
+        if (File.Exists(_tempFile)) File.Delete(_tempFile);
+        if (File.Exists(_tempFile + ".tmp")) File.Delete(_tempFile + ".tmp");
+    }
+
+    private BrandingRepository CreateRepository() => new(_tempFile);
+
+    [Fact]
+    public async Task LoadAsync_MissingFile_ReturnsDefaultBrandingSettings()
+    {
+        var repo = CreateRepository();
+
+        var settings = await repo.LoadAsync();
+
+        Assert.Null(settings.MspLogo);
+    }
+
+    [Fact]
+    public async Task SaveAndLoad_RoundTrips_MspLogo()
+    {
+        var repo = CreateRepository();
+        var logo = new LogoData { Base64 = "abc123==", MimeType = "image/png" };
+        var original = new BrandingSettings { MspLogo = logo };
+
+        await repo.SaveAsync(original);
+        var loaded = await repo.LoadAsync();
+
+        Assert.NotNull(loaded.MspLogo);
+        Assert.Equal("abc123==", loaded.MspLogo.Base64);
+        Assert.Equal("image/png", loaded.MspLogo.MimeType);
+    }
+
+    [Fact]
+    public async Task SaveAsync_CreatesDirectoryIfNotExists()
+    {
+        var tempDir = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName(), "subdir");
+        var filePath = Path.Combine(tempDir, "branding.json");
+        var repo = new BrandingRepository(filePath);
+
+        try
+        {
+            await repo.SaveAsync(new BrandingSettings());
+            Assert.True(File.Exists(filePath), "File must be created even when directory did not exist");
+        }
+        finally
+        {
+            if (File.Exists(filePath)) File.Delete(filePath);
+            if (Directory.Exists(tempDir)) Directory.Delete(tempDir, recursive: true);
+        }
+    }
+
+    [Fact]
+    public async Task TenantProfile_WithClientLogo_SerializesAndDeserializesCorrectly()
+    {
+        var logo = new LogoData { Base64 = "xyz==", MimeType = "image/jpeg" };
+        var profile = new TenantProfile
+        {
+            Name = "Contoso",
+            TenantUrl = "https://contoso.sharepoint.com",
+            ClientId = "client-id-123",
+            ClientLogo = logo
+        };
+
+        var options = new JsonSerializerOptions
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            WriteIndented = true
+        };
+        var json = JsonSerializer.Serialize(profile, options);
+
+        // Verify camelCase key exists
+        using var doc = JsonDocument.Parse(json);
+        Assert.True(doc.RootElement.TryGetProperty("clientLogo", out var clientLogoElem),
+            "JSON must contain 'clientLogo' key (camelCase)");
+        Assert.Equal(JsonValueKind.Object, clientLogoElem.ValueKind);
+
+        // Deserialize back
+        var readOptions = new JsonSerializerOptions { PropertyNameCaseInsensitive = true };
+        var loaded = JsonSerializer.Deserialize<TenantProfile>(json, readOptions);
+
+        Assert.NotNull(loaded?.ClientLogo);
+        Assert.Equal("xyz==", loaded.ClientLogo.Base64);
+        Assert.Equal("image/jpeg", loaded.ClientLogo.MimeType);
+    }
+
+    [Fact]
+    public async Task TenantProfile_WithoutClientLogo_SerializesWithNullAndDeserializesWithNull()
+    {
+        var profile = new TenantProfile
+        {
+            Name = "Fabrikam",
+            TenantUrl = "https://fabrikam.sharepoint.com",
+            ClientId = "client-id-456"
+        };
+
+        var options = new JsonSerializerOptions
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+            WriteIndented = true
+        };
+        var json = JsonSerializer.Serialize(profile, options);
+
+        // Deserialize back — ClientLogo should be null (forward compatible)
+        var readOptions = new JsonSerializerOptions { PropertyNameCaseInsensitive = true };
+        var loaded = JsonSerializer.Deserialize<TenantProfile>(json, readOptions);
+
+        Assert.NotNull(loaded);
+        Assert.Null(loaded.ClientLogo);
+    }
+}