feat(09-03): extend StorageViewModel with chart data properties and toggle

- Add IsDonutChart toggle, FileTypeMetrics collection, PieChartSeries, BarChartSeries, BarXAxes, BarYAxes
- Add UpdateChartSeries method with top-10 + Other aggregation
- Call CollectFileTypeMetricsAsync after storage scan in RunOperationAsync
- Clear chart data on tenant switch

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

SharepointToolbox/ViewModels/Tabs/StorageViewModel.cs

@@ -3,11 +3,15 @@ using System.Diagnostics;
 using System.Windows;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
+using LiveChartsCore;
+using LiveChartsCore.SkiaSharpView;
+using LiveChartsCore.SkiaSharpView.Painting;
 using Microsoft.Extensions.Logging;
 using Microsoft.Win32;
 using SharepointToolbox.Core.Models;
 using SharepointToolbox.Services;
 using SharepointToolbox.Services.Export;
+using SkiaSharp;
 
 namespace SharepointToolbox.ViewModels.Tabs;
 
@@ -33,6 +37,51 @@ public partial class StorageViewModel : FeatureViewModelBase
     [ObservableProperty]
     private int _folderDepth;
 
+    [ObservableProperty]
+    private bool _isDonutChart = true;
+
+    private ObservableCollection<FileTypeMetric> _fileTypeMetrics = new();
+    public ObservableCollection<FileTypeMetric> FileTypeMetrics
+    {
+        get => _fileTypeMetrics;
+        private set
+        {
+            _fileTypeMetrics = value;
+            OnPropertyChanged();
+            UpdateChartSeries();
+        }
+    }
+
+    public bool HasChartData => FileTypeMetrics.Count > 0;
+
+    private IEnumerable<ISeries> _pieChartSeries = Enumerable.Empty<ISeries>();
+    public IEnumerable<ISeries> PieChartSeries
+    {
+        get => _pieChartSeries;
+        private set { _pieChartSeries = value; OnPropertyChanged(); }
+    }
+
+    private IEnumerable<ISeries> _barChartSeries = Enumerable.Empty<ISeries>();
+    public IEnumerable<ISeries> BarChartSeries
+    {
+        get => _barChartSeries;
+        private set { _barChartSeries = value; OnPropertyChanged(); }
+    }
+
+    private Axis[] _barXAxes = Array.Empty<Axis>();
+    public Axis[] BarXAxes
+    {
+        get => _barXAxes;
+        private set { _barXAxes = value; OnPropertyChanged(); }
+    }
+
+    private Axis[] _barYAxes = Array.Empty<Axis>();
+    public Axis[] BarYAxes
+    {
+        get => _barYAxes;
+        private set { _barYAxes = value; OnPropertyChanged(); }
+    }
+
     public bool IsMaxDepth
     {
         get => FolderDepth >= 999;
@@ -163,6 +212,22 @@ public partial class StorageViewModel : FeatureViewModelBase
         {
             Results = new ObservableCollection<StorageNode>(flat);
         }
+
+        // Collect file-type metrics for chart visualization
+        progress.Report(OperationProgress.Indeterminate("Scanning file types for chart..."));
+        var typeMetrics = await _storageService.CollectFileTypeMetricsAsync(ctx, progress, ct);
+
+        if (Application.Current?.Dispatcher is { } chartDispatcher)
+        {
+            await chartDispatcher.InvokeAsync(() =>
+            {
+                FileTypeMetrics = new ObservableCollection<FileTypeMetric>(typeMetrics);
+            });
+        }
+        else
+        {
+            FileTypeMetrics = new ObservableCollection<FileTypeMetric>(typeMetrics);
+        }
     }
 
     protected override void OnTenantSwitched(TenantProfile profile)
@@ -170,6 +235,7 @@ public partial class StorageViewModel : FeatureViewModelBase
         _currentProfile = profile;
         _hasLocalSiteOverride = false;
         Results = new ObservableCollection<StorageNode>();
+        FileTypeMetrics = new ObservableCollection<FileTypeMetric>();
         SiteUrl = string.Empty;
         OnPropertyChanged(nameof(CurrentProfile));
         ExportCsvCommand.NotifyCanExecuteChanged();
@@ -229,6 +295,88 @@ public partial class StorageViewModel : FeatureViewModelBase
         }
     }
 
+    partial void OnIsDonutChartChanged(bool value)
+    {
+        UpdateChartSeries();
+    }
+
+    private void UpdateChartSeries()
+    {
+        var metrics = FileTypeMetrics.ToList();
+        OnPropertyChanged(nameof(HasChartData));
+
+        if (metrics.Count == 0)
+        {
+            PieChartSeries = Enumerable.Empty<ISeries>();
+            BarChartSeries = Enumerable.Empty<ISeries>();
+            BarXAxes = Array.Empty<Axis>();
+            BarYAxes = Array.Empty<Axis>();
+            return;
+        }
+
+        // Take top 10 by size, aggregate the rest as "Other"
+        var top = metrics.Take(10).ToList();
+        long otherSize = metrics.Skip(10).Sum(m => m.TotalSizeBytes);
+        int otherCount = metrics.Skip(10).Sum(m => m.FileCount);
+
+        var chartItems = new List<FileTypeMetric>(top);
+        if (otherSize > 0)
+            chartItems.Add(new FileTypeMetric("Other", otherSize, otherCount));
+
+        // Pie/Donut series
+        double innerRadius = IsDonutChart ? 50 : 0;
+        PieChartSeries = chartItems.Select(m => new PieSeries<long>
+        {
+            Values = new[] { m.TotalSizeBytes },
+            Name = m.DisplayLabel,
+            InnerRadius = innerRadius,
+            DataLabelsPosition = LiveChartsCore.Measure.PolarLabelsPosition.Outer,
+            DataLabelsFormatter = point => m.DisplayLabel,
+            ToolTipLabelFormatter = point =>
+                $"{m.DisplayLabel}: {FormatBytes(m.TotalSizeBytes)} ({m.FileCount} files)"
+        }).ToList();
+
+        // Bar chart series
+        BarChartSeries = new ISeries[]
+        {
+            new ColumnSeries<long>
+            {
+                Values = chartItems.Select(m => m.TotalSizeBytes).ToArray(),
+                Name = "Size",
+                DataLabelsFormatter = point =>
+                {
+                    int idx = (int)point.Index;
+                    return idx < chartItems.Count ? FormatBytes(chartItems[idx].TotalSizeBytes) : "";
+                }
+            }
+        };
+
+        BarXAxes = new Axis[]
+        {
+            new Axis
+            {
+                Labels = chartItems.Select(m => m.DisplayLabel).ToArray(),
+                LabelsRotation = -45
+            }
+        };
+
+        BarYAxes = new Axis[]
+        {
+            new Axis
+            {
+                Labeler = value => FormatBytes((long)value)
+            }
+        };
+    }
+
+    private static string FormatBytes(long bytes)
+    {
+        if (bytes < 1024) return $"{bytes} B";
+        if (bytes < 1024 * 1024) return $"{bytes / 1024.0:F1} KB";
+        if (bytes < 1024 * 1024 * 1024) return $"{bytes / (1024.0 * 1024):F1} MB";
+        return $"{bytes / (1024.0 * 1024 * 1024):F2} GB";
+    }
+
     private static void FlattenNode(StorageNode node, int level, List<StorageNode> result)
     {
         node.IndentLevel = level;