- Added ReportBranding? branding = null to BuildHtml on all 5 services
- Added ReportBranding? branding = null after CancellationToken ct on all WriteAsync overloads
- Injected BrandingHtmlHelper.BuildBrandingHeader(branding) between <body> and <h1> in each
- StorageHtmlExportService both overloads updated (nodes-only and nodes+fileTypeMetrics)
- HtmlExportService both overloads updated (PermissionEntry and SimplifiedPermissionEntry)
- Build passes with 0 warnings — all existing callers compile unchanged via default null
- Replace stub with full grouped HTML export (port of PS Export-DuplicatesToHTML)
- One collapsible card per DuplicateGroup with item count badge and path table
- Uses System.IO.File explicitly per WPF project pattern
- 3/3 DuplicatesHtmlExportServiceTests pass; 9/9 total export tests pass