feat(03-08): create DuplicatesViewModel, DuplicatesView XAML and code-behind

- DuplicatesViewModel: ModeFiles/Folders, criteria checkboxes, group flattening to DuplicateRow
- Uses TenantProfile site URL override pattern (ctx.Url is read-only)
- ExportHtmlCommand exports DuplicateGroup list via DuplicatesHtmlExportService
- DuplicatesView.xaml: type selector, criteria panel + flattened DataGrid
- DuplicatesView.xaml.cs: DI constructor with DataContext wiring

SharepointToolbox/ViewModels/Tabs/DuplicatesViewModel.cs

@@ -0,0 +1,169 @@
+using System.Collections.ObjectModel;
+using System.Diagnostics;
+using System.Windows;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Microsoft.Extensions.Logging;
+using Microsoft.Win32;
+using SharepointToolbox.Core.Models;
+using SharepointToolbox.Services;
+using SharepointToolbox.Services.Export;
+
+namespace SharepointToolbox.ViewModels.Tabs;
+
+/// <summary>Flat display row wrapping a DuplicateItem with its group name.</summary>
+public class DuplicateRow
+{
+    public string GroupName { get; set; } = string.Empty;
+    public string Name { get; set; } = string.Empty;
+    public string Path { get; set; } = string.Empty;
+    public string Library { get; set; } = string.Empty;
+    public long? SizeBytes { get; set; }
+    public DateTime? Created { get; set; }
+    public DateTime? Modified { get; set; }
+    public int? FolderCount { get; set; }
+    public int? FileCount { get; set; }
+    public int GroupSize { get; set; }
+}
+
+public partial class DuplicatesViewModel : FeatureViewModelBase
+{
+    private readonly IDuplicatesService _duplicatesService;
+    private readonly ISessionManager _sessionManager;
+    private readonly DuplicatesHtmlExportService _htmlExportService;
+    private readonly ILogger<FeatureViewModelBase> _logger;
+    private TenantProfile? _currentProfile;
+    private IReadOnlyList<DuplicateGroup> _lastGroups = Array.Empty<DuplicateGroup>();
+
+    [ObservableProperty] private string _siteUrl = string.Empty;
+    [ObservableProperty] private bool _modeFiles = true;
+    [ObservableProperty] private bool _modeFolders;
+    [ObservableProperty] private bool _matchSize = true;
+    [ObservableProperty] private bool _matchCreated;
+    [ObservableProperty] private bool _matchModified;
+    [ObservableProperty] private bool _matchSubfolders;
+    [ObservableProperty] private bool _matchFileCount;
+    [ObservableProperty] private bool _includeSubsites;
+    [ObservableProperty] private string _library = string.Empty;
+
+    private ObservableCollection<DuplicateRow> _results = new();
+    public ObservableCollection<DuplicateRow> Results
+    {
+        get => _results;
+        private set
+        {
+            _results = value;
+            OnPropertyChanged();
+            ExportHtmlCommand.NotifyCanExecuteChanged();
+        }
+    }
+
+    public IAsyncRelayCommand ExportHtmlCommand { get; }
+    public TenantProfile? CurrentProfile => _currentProfile;
+
+    public DuplicatesViewModel(
+        IDuplicatesService duplicatesService,
+        ISessionManager sessionManager,
+        DuplicatesHtmlExportService htmlExportService,
+        ILogger<FeatureViewModelBase> logger)
+        : base(logger)
+    {
+        _duplicatesService = duplicatesService;
+        _sessionManager    = sessionManager;
+        _htmlExportService = htmlExportService;
+        _logger            = logger;
+
+        ExportHtmlCommand = new AsyncRelayCommand(ExportHtmlAsync, CanExport);
+    }
+
+    protected override async Task RunOperationAsync(CancellationToken ct, IProgress<OperationProgress> progress)
+    {
+        if (_currentProfile == null)
+        {
+            StatusMessage = "No tenant selected. Please connect to a tenant first.";
+            return;
+        }
+        if (string.IsNullOrWhiteSpace(SiteUrl))
+        {
+            StatusMessage = "Please enter a site URL.";
+            return;
+        }
+
+        var siteProfile = new TenantProfile
+        {
+            TenantUrl = SiteUrl.TrimEnd('/'),
+            ClientId  = _currentProfile.ClientId,
+            Name      = _currentProfile.Name
+        };
+        var ctx = await _sessionManager.GetOrCreateContextAsync(siteProfile, ct);
+
+        var opts = new DuplicateScanOptions(
+            Mode:               ModeFiles ? "Files" : "Folders",
+            MatchSize:          MatchSize,
+            MatchCreated:       MatchCreated,
+            MatchModified:      MatchModified,
+            MatchSubfolderCount: MatchSubfolders,
+            MatchFileCount:     MatchFileCount,
+            IncludeSubsites:    IncludeSubsites,
+            Library:            string.IsNullOrWhiteSpace(Library) ? null : Library
+        );
+
+        var groups = await _duplicatesService.ScanDuplicatesAsync(ctx, opts, progress, ct);
+        _lastGroups = groups;
+
+        // Flatten groups to display rows
+        var rows = groups
+            .SelectMany(g => g.Items.Select(item => new DuplicateRow
+            {
+                GroupName   = g.Name,
+                Name        = item.Name,
+                Path        = item.Path,
+                Library     = item.Library,
+                SizeBytes   = item.SizeBytes,
+                Created     = item.Created,
+                Modified    = item.Modified,
+                FolderCount = item.FolderCount,
+                FileCount   = item.FileCount,
+                GroupSize   = g.Items.Count
+            }))
+            .ToList();
+
+        if (Application.Current?.Dispatcher is { } dispatcher)
+            await dispatcher.InvokeAsync(() => Results = new ObservableCollection<DuplicateRow>(rows));
+        else
+            Results = new ObservableCollection<DuplicateRow>(rows);
+    }
+
+    protected override void OnTenantSwitched(Core.Models.TenantProfile profile)
+    {
+        _currentProfile = profile;
+        Results = new ObservableCollection<DuplicateRow>();
+        _lastGroups = Array.Empty<DuplicateGroup>();
+        SiteUrl = string.Empty;
+        OnPropertyChanged(nameof(CurrentProfile));
+        ExportHtmlCommand.NotifyCanExecuteChanged();
+    }
+
+    internal void SetCurrentProfile(TenantProfile profile) => _currentProfile = profile;
+
+    private bool CanExport() => _lastGroups.Count > 0;
+
+    private async Task ExportHtmlAsync()
+    {
+        if (_lastGroups.Count == 0) return;
+        var dialog = new SaveFileDialog
+        {
+            Title = "Export duplicates report to HTML",
+            Filter = "HTML files (*.html)|*.html|All files (*.*)|*.*",
+            DefaultExt = "html",
+            FileName = "duplicates_report"
+        };
+        if (dialog.ShowDialog() != true) return;
+        try
+        {
+            await _htmlExportService.WriteAsync(_lastGroups, dialog.FileName, CancellationToken.None);
+            Process.Start(new ProcessStartInfo(dialog.FileName) { UseShellExecute = true });
+        }
+        catch (Exception ex) { StatusMessage = $"Export failed: {ex.Message}"; _logger.LogError(ex, "HTML export failed."); }
+    }
+}

SharepointToolbox/Views/Tabs/DuplicatesView.xaml

@@ -0,0 +1,77 @@
+<UserControl x:Class="SharepointToolbox.Views.Tabs.DuplicatesView"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:loc="clr-namespace:SharepointToolbox.Localization">
+    <DockPanel LastChildFill="True">
+        <!-- Options panel -->
+        <ScrollViewer DockPanel.Dock="Left" Width="240" VerticalScrollBarVisibility="Auto" Margin="8,8,4,8">
+            <StackPanel>
+                <Label Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[lbl.site.url]}" />
+                <TextBox Text="{Binding SiteUrl, UpdateSourceTrigger=PropertyChanged}"
+                         IsEnabled="{Binding IsRunning, Converter={StaticResource InverseBoolConverter}}"
+                         Height="26" Margin="0,0,0,8" />
+
+                <GroupBox Header="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[grp.dup.type]}" Margin="0,0,0,8">
+                    <StackPanel Margin="4">
+                        <RadioButton Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[rad.dup.files]}"
+                                     IsChecked="{Binding ModeFiles}" Margin="0,2" />
+                        <RadioButton Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[rad.dup.folders]}"
+                                     IsChecked="{Binding ModeFolders}" Margin="0,2" />
+                    </StackPanel>
+                </GroupBox>
+
+                <GroupBox Header="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[grp.dup.criteria]}" Margin="0,0,0,8">
+                    <StackPanel Margin="4">
+                        <TextBlock Text="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[lbl.dup.note]}"
+                                   TextWrapping="Wrap" FontSize="11" Foreground="#555" Margin="0,0,0,6" />
+                        <CheckBox Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[chk.dup.size]}"
+                                  IsChecked="{Binding MatchSize}" Margin="0,2" />
+                        <CheckBox Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[chk.dup.created]}"
+                                  IsChecked="{Binding MatchCreated}" Margin="0,2" />
+                        <CheckBox Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[chk.dup.modified]}"
+                                  IsChecked="{Binding MatchModified}" Margin="0,2" />
+                        <CheckBox Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[chk.dup.subfolders]}"
+                                  IsChecked="{Binding MatchSubfolders}" Margin="0,2" />
+                        <CheckBox Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[chk.dup.filecount]}"
+                                  IsChecked="{Binding MatchFileCount}" Margin="0,2" />
+                    </StackPanel>
+                </GroupBox>
+
+                <Label Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[lbl.library]}" />
+                <TextBox Text="{Binding Library, UpdateSourceTrigger=PropertyChanged}" Height="26"
+                         ToolTip="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[ph.dup.lib]}" Margin="0,0,0,6" />
+
+                <CheckBox Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[chk.include.subsites]}"
+                          IsChecked="{Binding IncludeSubsites}" Margin="0,4,0,8" />
+
+                <Button Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[btn.run.scan]}"
+                        Command="{Binding RunCommand}" Height="28" Margin="0,0,0,4" />
+                <Button Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[btn.cancel]}"
+                        Command="{Binding CancelCommand}" Height="28" Margin="0,0,0,8" />
+
+                <Button Content="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[btn.open.results]}"
+                        Command="{Binding ExportHtmlCommand}" Height="28" Margin="0,0,0,4" />
+
+                <TextBlock Text="{Binding StatusMessage}" TextWrapping="Wrap" FontSize="11" Foreground="#555" Margin="0,4" />
+            </StackPanel>
+        </ScrollViewer>
+
+        <!-- Results DataGrid -->
+        <DataGrid ItemsSource="{Binding Results}" IsReadOnly="True" AutoGenerateColumns="False"
+                  VirtualizingPanel.IsVirtualizing="True" Margin="4,8,8,8">
+            <DataGrid.Columns>
+                <DataGridTextColumn Header="Group" Binding="{Binding GroupName}" Width="160" />
+                <DataGridTextColumn Header="Copies" Binding="{Binding GroupSize}" Width="60"
+                                    ElementStyle="{StaticResource RightAlignStyle}" />
+                <DataGridTextColumn Header="Name" Binding="{Binding Name}" Width="160" />
+                <DataGridTextColumn Header="Library" Binding="{Binding Library}" Width="120" />
+                <DataGridTextColumn Header="Size"
+                                    Binding="{Binding SizeBytes, Converter={StaticResource BytesConverter}}"
+                                    Width="90" ElementStyle="{StaticResource RightAlignStyle}" />
+                <DataGridTextColumn Header="Created" Binding="{Binding Created, StringFormat=yyyy-MM-dd}" Width="100" />
+                <DataGridTextColumn Header="Modified" Binding="{Binding Modified, StringFormat=yyyy-MM-dd}" Width="100" />
+                <DataGridTextColumn Header="Path" Binding="{Binding Path}" Width="*" />
+            </DataGrid.Columns>
+        </DataGrid>
+    </DockPanel>
+</UserControl>

SharepointToolbox/Views/Tabs/DuplicatesView.xaml.cs

@@ -0,0 +1,12 @@
+using System.Windows.Controls;
+
+namespace SharepointToolbox.Views.Tabs;
+
+public partial class DuplicatesView : UserControl
+{
+    public DuplicatesView(ViewModels.Tabs.DuplicatesViewModel viewModel)
+    {
+        InitializeComponent();
+        DataContext = viewModel;
+    }
+}