feat(11-01): add ReportBranding model and BrandingHtmlHelper with tests

- Add ReportBranding positional record bundling MspLogo and ClientLogo
- Add BrandingHtmlHelper static class generating flex branding header HTML
- Add BrandingHtmlHelperTests covering all 4 logo states (null, both null, single, both)
- Add InternalsVisibleTo for SharepointToolbox.Tests in project file

SharepointToolbox.Tests/Services/Export/BrandingHtmlHelperTests.cs

@@ -0,0 +1,105 @@
+using SharepointToolbox.Core.Models;
+using SharepointToolbox.Services.Export;
+using Xunit;
+
+namespace SharepointToolbox.Tests.Services.Export;
+
+[Trait("Category", "Unit")]
+public class BrandingHtmlHelperTests
+{
+    private static LogoData MakeLogo(string mime = "image/png", string base64 = "dGVzdA==") =>
+        new() { MimeType = mime, Base64 = base64 };
+
+    // Test 1: null ReportBranding returns empty string
+    [Fact]
+    public void BuildBrandingHeader_NullBranding_ReturnsEmptyString()
+    {
+        var result = BrandingHtmlHelper.BuildBrandingHeader(null);
+        Assert.Equal(string.Empty, result);
+    }
+
+    // Test 2: both logos null returns empty string
+    [Fact]
+    public void BuildBrandingHeader_BothLogosNull_ReturnsEmptyString()
+    {
+        var branding = new ReportBranding(null, null);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+        Assert.Equal(string.Empty, result);
+    }
+
+    // Test 3: only MspLogo — contains MSP img tag, no second img
+    [Fact]
+    public void BuildBrandingHeader_OnlyMspLogo_ReturnsHtmlWithOneImg()
+    {
+        var msp = MakeLogo("image/png", "bXNwbG9nbw==");
+        var branding = new ReportBranding(msp, null);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+
+        Assert.Contains("data:image/png;base64,bXNwbG9nbw==", result);
+        Assert.Single(result.Split("<img", StringSplitOptions.None).Skip(1).ToArray());
+    }
+
+    // Test 4: only ClientLogo — contains client img tag, no flex spacer div
+    [Fact]
+    public void BuildBrandingHeader_OnlyClientLogo_ReturnsHtmlWithOneImgNoSpacer()
+    {
+        var client = MakeLogo("image/jpeg", "Y2xpZW50bG9nbw==");
+        var branding = new ReportBranding(null, client);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+
+        Assert.Contains("data:image/jpeg;base64,Y2xpZW50bG9nbw==", result);
+        Assert.Single(result.Split("<img", StringSplitOptions.None).Skip(1).ToArray());
+        Assert.DoesNotContain("flex:1", result);
+    }
+
+    // Test 5: both logos — two img tags and a flex spacer div between them
+    [Fact]
+    public void BuildBrandingHeader_BothLogos_ReturnsHtmlWithTwoImgsAndSpacer()
+    {
+        var msp = MakeLogo("image/png", "bXNw");
+        var client = MakeLogo("image/jpeg", "Y2xpZW50");
+        var branding = new ReportBranding(msp, client);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+
+        Assert.Contains("data:image/png;base64,bXNw", result);
+        Assert.Contains("data:image/jpeg;base64,Y2xpZW50", result);
+        Assert.Equal(2, result.Split("<img", StringSplitOptions.None).Length - 1);
+        Assert.Contains("flex:1", result);
+    }
+
+    // Test 6: img tags use inline data-URI format
+    [Fact]
+    public void BuildBrandingHeader_WithMspLogo_UsesDataUriFormat()
+    {
+        var msp = MakeLogo("image/png", "dGVzdA==");
+        var branding = new ReportBranding(msp, null);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+
+        Assert.Contains("src=\"data:image/png;base64,dGVzdA==\"", result);
+    }
+
+    // Test 7: img tags have max-height:60px and max-width:200px styles
+    [Fact]
+    public void BuildBrandingHeader_WithLogo_ImgHasCorrectDimensions()
+    {
+        var msp = MakeLogo();
+        var branding = new ReportBranding(msp, null);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+
+        Assert.Contains("max-height:60px", result);
+        Assert.Contains("max-width:200px", result);
+    }
+
+    // Test 8: outer div uses display:flex;gap:16px;align-items:center
+    [Fact]
+    public void BuildBrandingHeader_WithLogo_OuterDivUsesFlexLayout()
+    {
+        var msp = MakeLogo();
+        var branding = new ReportBranding(msp, null);
+        var result = BrandingHtmlHelper.BuildBrandingHeader(branding);
+
+        Assert.Contains("display:flex", result);
+        Assert.Contains("gap:16px", result);
+        Assert.Contains("align-items:center", result);
+    }
+}

SharepointToolbox/Core/Models/ReportBranding.cs

@@ -0,0 +1,8 @@
+namespace SharepointToolbox.Core.Models;
+
+/// <summary>
+/// Bundles MSP and client logos for passing to export services.
+/// Export services receive this as a simple DTO — they don't know
+/// about IBrandingService or ProfileService.
+/// </summary>
+public record ReportBranding(LogoData? MspLogo, LogoData? ClientLogo);

SharepointToolbox/Services/Export/BrandingHtmlHelper.cs

@@ -0,0 +1,37 @@
+using System.Text;
+using SharepointToolbox.Core.Models;
+
+namespace SharepointToolbox.Services.Export;
+
+/// <summary>
+/// Generates the branding header HTML fragment for HTML reports.
+/// Called by each HTML export service between &lt;body&gt; and &lt;h1&gt;.
+/// Returns empty string when no logos are configured (no broken images).
+/// </summary>
+internal static class BrandingHtmlHelper
+{
+    public static string BuildBrandingHeader(ReportBranding? branding)
+    {
+        if (branding is null) return string.Empty;
+
+        var msp = branding.MspLogo;
+        var client = branding.ClientLogo;
+
+        if (msp is null && client is null) return string.Empty;
+
+        var sb = new StringBuilder();
+        sb.AppendLine("<div style=\"display:flex;gap:16px;align-items:center;padding:12px 24px 0;\">");
+
+        if (msp is not null)
+            sb.AppendLine($"  <img src=\"data:{msp.MimeType};base64,{msp.Base64}\" alt=\"\" style=\"max-height:60px;max-width:200px;object-fit:contain;\">");
+
+        if (msp is not null && client is not null)
+            sb.AppendLine("  <div style=\"flex:1\"></div>");
+
+        if (client is not null)
+            sb.AppendLine($"  <img src=\"data:{client.MimeType};base64,{client.Base64}\" alt=\"\" style=\"max-height:60px;max-width:200px;object-fit:contain;\">");
+
+        sb.AppendLine("</div>");
+        return sb.ToString();
+    }
+}

SharepointToolbox/SharepointToolbox.csproj

@@ -18,6 +18,12 @@
     <IncludeNativeLibrariesForSelfExtract>true</IncludeNativeLibrariesForSelfExtract>
   </PropertyGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleToAttribute">
+      <_Parameter1>SharepointToolbox.Tests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
   <ItemGroup>
     <ApplicationDefinition Remove="App.xaml" />
     <Page Include="App.xaml" />