feat(12-01): add Base64ToImageSourceConverter, localization keys, and ClientLogoPreview property

- Base64ToImageSourceConverter converts data URI strings to BitmapImage with null-safe error handling
- Registered converter in App.xaml as Base64ToImageConverter global resource
- Added 9 localization keys (EN+FR) for logo UI labels in Settings and Profile dialogs
- Added ClientLogoPreview string property to ProfileManagementViewModel with FormatLogoPreview helper
- Updated OnSelectedProfileChanged, BrowseClientLogoAsync, ClearClientLogoAsync, AutoPullClientLogoAsync
- 17 tests pass (6 converter + 11 profile VM logo tests)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SharepointToolbox.Tests/Converters/Base64ToImageSourceConverterTests.cs

@@ -0,0 +1,53 @@
+using System.Globalization;
+using SharepointToolbox.Views.Converters;
+
+namespace SharepointToolbox.Tests.Converters;
+
+[Trait("Category", "Unit")]
+public class Base64ToImageSourceConverterTests
+{
+    private readonly Base64ToImageSourceConverter _converter = new();
+
+    [Fact]
+    public void Convert_NullValue_ReturnsNull()
+    {
+        var result = _converter.Convert(null, typeof(object), null, CultureInfo.InvariantCulture);
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Convert_EmptyString_ReturnsNull()
+    {
+        var result = _converter.Convert(string.Empty, typeof(object), null, CultureInfo.InvariantCulture);
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Convert_NonStringValue_ReturnsNull()
+    {
+        var result = _converter.Convert(42, typeof(object), null, CultureInfo.InvariantCulture);
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Convert_MalformedString_NoBase64Marker_ReturnsNull()
+    {
+        var result = _converter.Convert("not-a-data-uri", typeof(object), null, CultureInfo.InvariantCulture);
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void Convert_InvalidBase64AfterMarker_ReturnsNull()
+    {
+        // Has the marker but invalid base64 content — should not throw
+        var result = _converter.Convert("data:image/png;base64,!!!invalid!!!", typeof(object), null, CultureInfo.InvariantCulture);
+        Assert.Null(result);
+    }
+
+    [Fact]
+    public void ConvertBack_ThrowsNotImplementedException()
+    {
+        Assert.Throws<NotImplementedException>(() =>
+            _converter.ConvertBack(null, typeof(object), null, CultureInfo.InvariantCulture));
+    }
+}

SharepointToolbox.Tests/ViewModels/ProfileManagementViewModelLogoTests.cs

@@ -115,4 +115,71 @@ public class ProfileManagementViewModelLogoTests : IDisposable
         var persisted = profiles.First(p => p.Name == "TestTenant");
         Assert.Null(persisted.ClientLogo);
     }
+
+    [Fact]
+    public void ClientLogoPreview_IsNull_WhenNoProfileSelected()
+    {
+        var vm = CreateViewModel();
+        Assert.Null(vm.ClientLogoPreview);
+    }
+
+    [Fact]
+    public void ClientLogoPreview_UpdatesToDataUri_WhenProfileWithLogoSelected()
+    {
+        var vm = CreateViewModel();
+        var profile = new TenantProfile
+        {
+            Name = "WithLogo",
+            TenantUrl = "https://test.sharepoint.com",
+            ClientId = "00000000-0000-0000-0000-000000000002",
+            ClientLogo = new LogoData { Base64 = "dGVzdA==", MimeType = "image/png" }
+        };
+
+        vm.SelectedProfile = profile;
+
+        Assert.Equal("data:image/png;base64,dGVzdA==", vm.ClientLogoPreview);
+    }
+
+    [Fact]
+    public void ClientLogoPreview_IsNull_WhenProfileWithoutLogoSelected()
+    {
+        var vm = CreateViewModel();
+        var profile = new TenantProfile
+        {
+            Name = "NoLogo",
+            TenantUrl = "https://test.sharepoint.com",
+            ClientId = "00000000-0000-0000-0000-000000000003"
+        };
+
+        vm.SelectedProfile = profile;
+
+        Assert.Null(vm.ClientLogoPreview);
+    }
+
+    [Fact]
+    public async Task ClearClientLogoCommand_SetsClientLogoPreviewToNull()
+    {
+        var profileService = new ProfileService(new ProfileRepository(_tempFile));
+        var profile = new TenantProfile
+        {
+            Name = "ClearTest",
+            TenantUrl = "https://test.sharepoint.com",
+            ClientId = "00000000-0000-0000-0000-000000000004",
+            ClientLogo = new LogoData { Base64 = "dGVzdA==", MimeType = "image/png" }
+        };
+        await profileService.AddProfileAsync(profile);
+
+        var vm = new ProfileManagementViewModel(
+            profileService,
+            _mockBranding.Object,
+            _graphClientFactory,
+            _logger);
+
+        vm.SelectedProfile = profile;
+        Assert.NotNull(vm.ClientLogoPreview);
+
+        await vm.ClearClientLogoCommand.ExecuteAsync(null);
+
+        Assert.Null(vm.ClientLogoPreview);
+    }
 }

SharepointToolbox/App.xaml

@@ -11,6 +11,7 @@
         <conv:EnumBoolConverter          x:Key="EnumBoolConverter" />
         <conv:StringToVisibilityConverter x:Key="StringToVisibilityConverter" />
         <conv:ListToStringConverter      x:Key="ListToStringConverter" />
+        <conv:Base64ToImageSourceConverter x:Key="Base64ToImageConverter" />
         <Style x:Key="RightAlignStyle" TargetType="TextBlock">
             <Setter Property="HorizontalAlignment" Value="Right" />
         </Style>

SharepointToolbox/Localization/Strings.fr.resx

@@ -384,4 +384,14 @@
   <data name="stor.chart.bar" xml:space="preserve"><value>Graphique en barres</value></data>
   <data name="stor.chart.toggle" xml:space="preserve"><value>Type de graphique :</value></data>
   <data name="stor.chart.nodata" xml:space="preserve"><value>Ex&#233;cutez une analyse pour voir la r&#233;partition par type de fichier.</value></data>
+  <!-- Phase 12: Logo UI -->
+  <data name="settings.logo.title" xml:space="preserve"><value>Logo MSP</value></data>
+  <data name="settings.logo.browse" xml:space="preserve"><value>Importer</value></data>
+  <data name="settings.logo.clear" xml:space="preserve"><value>Effacer</value></data>
+  <data name="settings.logo.nopreview" xml:space="preserve"><value>Aucun logo configur&#233;</value></data>
+  <data name="profile.logo.title" xml:space="preserve"><value>Logo client</value></data>
+  <data name="profile.logo.browse" xml:space="preserve"><value>Importer</value></data>
+  <data name="profile.logo.clear" xml:space="preserve"><value>Effacer</value></data>
+  <data name="profile.logo.autopull" xml:space="preserve"><value>Importer depuis Entra</value></data>
+  <data name="profile.logo.nopreview" xml:space="preserve"><value>Aucun logo configur&#233;</value></data>
 </root>

SharepointToolbox/Localization/Strings.resx

@@ -384,4 +384,14 @@
   <data name="stor.chart.bar" xml:space="preserve"><value>Bar Chart</value></data>
   <data name="stor.chart.toggle" xml:space="preserve"><value>Chart View:</value></data>
   <data name="stor.chart.nodata" xml:space="preserve"><value>Run a storage scan to see file type breakdown.</value></data>
+  <!-- Phase 12: Logo UI -->
+  <data name="settings.logo.title" xml:space="preserve"><value>MSP Logo</value></data>
+  <data name="settings.logo.browse" xml:space="preserve"><value>Import</value></data>
+  <data name="settings.logo.clear" xml:space="preserve"><value>Clear</value></data>
+  <data name="settings.logo.nopreview" xml:space="preserve"><value>No logo configured</value></data>
+  <data name="profile.logo.title" xml:space="preserve"><value>Client Logo</value></data>
+  <data name="profile.logo.browse" xml:space="preserve"><value>Import</value></data>
+  <data name="profile.logo.clear" xml:space="preserve"><value>Clear</value></data>
+  <data name="profile.logo.autopull" xml:space="preserve"><value>Pull from Entra</value></data>
+  <data name="profile.logo.nopreview" xml:space="preserve"><value>No logo configured</value></data>
 </root>

SharepointToolbox/ViewModels/ProfileManagementViewModel.cs

@@ -32,6 +32,13 @@ public partial class ProfileManagementViewModel : ObservableObject
     [ObservableProperty]
     private string _validationMessage = string.Empty;
 
+    private string? _clientLogoPreview;
+    public string? ClientLogoPreview
+    {
+        get => _clientLogoPreview;
+        private set { _clientLogoPreview = value; OnPropertyChanged(); }
+    }
+
     public ObservableCollection<TenantProfile> Profiles { get; } = new();
 
     public IAsyncRelayCommand AddCommand { get; }
@@ -81,6 +88,7 @@ public partial class ProfileManagementViewModel : ObservableObject
 
     partial void OnSelectedProfileChanged(TenantProfile? value)
     {
+        ClientLogoPreview = FormatLogoPreview(value?.ClientLogo);
         BrowseClientLogoCommand.NotifyCanExecuteChanged();
         ClearClientLogoCommand.NotifyCanExecuteChanged();
         AutoPullClientLogoCommand.NotifyCanExecuteChanged();
@@ -88,6 +96,9 @@ public partial class ProfileManagementViewModel : ObservableObject
         DeleteCommand.NotifyCanExecuteChanged();
     }
 
+    private static string? FormatLogoPreview(LogoData? logo)
+        => logo is not null ? $"data:{logo.MimeType};base64,{logo.Base64}" : null;
+
     private void NotifyCommandsCanExecuteChanged()
     {
         AddCommand.NotifyCanExecuteChanged();
@@ -172,6 +183,7 @@ public partial class ProfileManagementViewModel : ObservableObject
         {
             var logo = await _brandingService.ImportLogoAsync(dialog.FileName);
             SelectedProfile.ClientLogo = logo;
+            ClientLogoPreview = FormatLogoPreview(logo);
             await _profileService.UpdateProfileAsync(SelectedProfile);
             ValidationMessage = string.Empty;
         }
@@ -188,6 +200,7 @@ public partial class ProfileManagementViewModel : ObservableObject
         try
         {
             SelectedProfile.ClientLogo = null;
+            ClientLogoPreview = null;
             await _profileService.UpdateProfileAsync(SelectedProfile);
             ValidationMessage = string.Empty;
         }
@@ -229,6 +242,7 @@ public partial class ProfileManagementViewModel : ObservableObject
 
             var logo = await _brandingService.ImportLogoFromBytesAsync(bytes);
             SelectedProfile.ClientLogo = logo;
+            ClientLogoPreview = FormatLogoPreview(logo);
             await _profileService.UpdateProfileAsync(SelectedProfile);
             ValidationMessage = "Client logo pulled from Entra branding.";
         }

SharepointToolbox/Views/Converters/Base64ToImageSourceConverter.cs

@@ -0,0 +1,46 @@
+using System.Globalization;
+using System.IO;
+using System.Windows.Data;
+using System.Windows.Media.Imaging;
+
+namespace SharepointToolbox.Views.Converters;
+
+/// <summary>
+/// Converts a data URI string (e.g. "data:image/png;base64,iVBOR...") to a BitmapImage
+/// for use with WPF Image controls. Returns null for null, empty, or malformed input.
+/// </summary>
+[ValueConversion(typeof(string), typeof(BitmapImage))]
+public class Base64ToImageSourceConverter : IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is not string dataUri || string.IsNullOrEmpty(dataUri))
+            return null;
+
+        try
+        {
+            var marker = "base64,";
+            var idx = dataUri.IndexOf(marker, StringComparison.Ordinal);
+            if (idx < 0) return null;
+
+            var base64 = dataUri[(idx + marker.Length)..];
+            var bytes = System.Convert.FromBase64String(base64);
+
+            var image = new BitmapImage();
+            using var ms = new MemoryStream(bytes);
+            image.BeginInit();
+            image.CacheOption = BitmapCacheOption.OnLoad;
+            image.StreamSource = ms;
+            image.EndInit();
+            image.Freeze();
+            return image;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+        => throw new NotImplementedException();
+}