feat(11-02): extend export tests to verify branding injection across all 5 services

- HtmlExportServiceTests: 3 new tests (MSP logo only, null branding no img, both logos)
- SearchExportServiceTests: 1 new branding test (img tag present when branding provided)
- StorageHtmlExportServiceTests: 1 new branding test (img tag present)
- DuplicatesHtmlExportServiceTests: 1 new branding test (img tag present)
- UserAccessHtmlExportServiceTests: 1 new branding test (img tag present)
- MakeBranding helper added to each test class
- All 45 export tests pass; full suite 247/247 with 0 failures

SharepointToolbox.Tests/Services/Export/StorageHtmlExportServiceTests.cs

@@ -6,6 +6,12 @@ namespace SharepointToolbox.Tests.Services.Export;
 
 public class StorageHtmlExportServiceTests
 {
+    private static ReportBranding MakeBranding(bool msp = true, bool client = false)
+    {
+        var mspLogo    = msp    ? new LogoData { Base64 = "bXNw", MimeType = "image/png" }  : null;
+        var clientLogo = client ? new LogoData { Base64 = "Y2xpZW50", MimeType = "image/jpeg" } : null;
+        return new ReportBranding(mspLogo, clientLogo);
+    }
     [Fact]
     public void BuildHtml_WithNodes_ContainsToggleJs()
     {
@@ -48,4 +54,18 @@ public class StorageHtmlExportServiceTests
         Assert.Contains("Documents", html);
         Assert.Contains("Images", html);
     }
+
+    // ── Branding tests ────────────────────────────────────────────────────────
+
+    [Fact]
+    public void BuildHtml_WithBranding_ContainsLogoImg()
+    {
+        var svc = new StorageHtmlExportService();
+        var nodes = new List<StorageNode>
+        {
+            new() { Name = "Documents", Library = "Documents", SiteTitle = "Site1", TotalSizeBytes = 1000 }
+        };
+        var html = svc.BuildHtml(nodes, MakeBranding(msp: true));
+        Assert.Contains("data:image/png;base64,bXNw", html);
+    }
 }