feat(06-04): update single-site tab VMs for global site consumption

- StorageViewModel: add OnGlobalSitesChanged, OnSiteUrlChanged, _hasLocalSiteOverride
- SearchViewModel: add OnGlobalSitesChanged, OnSiteUrlChanged, _hasLocalSiteOverride
- DuplicatesViewModel: add OnGlobalSitesChanged, OnSiteUrlChanged, _hasLocalSiteOverride
- FolderStructureViewModel: add OnGlobalSitesChanged, OnSiteUrlChanged, _hasLocalSiteOverride
- All four VMs pre-fill SiteUrl from first global site; local typing sets override flag
- Tenant switch resets _hasLocalSiteOverride in all four VMs

SharepointToolbox/ViewModels/Tabs/DuplicatesViewModel.cs

@@ -33,6 +33,7 @@ public partial class DuplicatesViewModel : FeatureViewModelBase
     private readonly DuplicatesHtmlExportService _htmlExportService;
     private readonly ILogger<FeatureViewModelBase> _logger;
     private TenantProfile? _currentProfile;
+    private bool _hasLocalSiteOverride;
     private IReadOnlyList<DuplicateGroup> _lastGroups = Array.Empty<DuplicateGroup>();
 
     [ObservableProperty] private string _siteUrl = string.Empty;
@@ -76,6 +77,26 @@ public partial class DuplicatesViewModel : FeatureViewModelBase
         ExportHtmlCommand = new AsyncRelayCommand(ExportHtmlAsync, CanExport);
     }
 
+    protected override void OnGlobalSitesChanged(IReadOnlyList<SiteInfo> sites)
+    {
+        if (_hasLocalSiteOverride) return;
+        SiteUrl = sites.Count > 0 ? sites[0].Url : string.Empty;
+    }
+
+    partial void OnSiteUrlChanged(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            _hasLocalSiteOverride = false;
+            if (GlobalSites.Count > 0)
+                SiteUrl = GlobalSites[0].Url;
+        }
+        else if (GlobalSites.Count == 0 || value != GlobalSites[0].Url)
+        {
+            _hasLocalSiteOverride = true;
+        }
+    }
+
     protected override async Task RunOperationAsync(CancellationToken ct, IProgress<OperationProgress> progress)
     {
         if (_currentProfile == null)
@@ -137,6 +158,7 @@ public partial class DuplicatesViewModel : FeatureViewModelBase
     protected override void OnTenantSwitched(Core.Models.TenantProfile profile)
     {
         _currentProfile = profile;
+        _hasLocalSiteOverride = false;
         Results = new ObservableCollection<DuplicateRow>();
         _lastGroups = Array.Empty<DuplicateGroup>();
         SiteUrl = string.Empty;

SharepointToolbox/ViewModels/Tabs/FolderStructureViewModel.cs

@@ -22,6 +22,7 @@ public partial class FolderStructureViewModel : FeatureViewModelBase
     private readonly BulkResultCsvExportService _exportService;
     private readonly ILogger<FeatureViewModelBase> _logger;
     private TenantProfile? _currentProfile;
+    private bool _hasLocalSiteOverride;
     private List<FolderStructureRow>? _validRows;
     private BulkOperationSummary<string>? _lastResult;
 
@@ -65,6 +66,26 @@ public partial class FolderStructureViewModel : FeatureViewModelBase
         ExportFailedCommand = new AsyncRelayCommand(ExportFailedAsync, () => HasFailures);
     }
 
+    protected override void OnGlobalSitesChanged(IReadOnlyList<SiteInfo> sites)
+    {
+        if (_hasLocalSiteOverride) return;
+        SiteUrl = sites.Count > 0 ? sites[0].Url : string.Empty;
+    }
+
+    partial void OnSiteUrlChanged(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            _hasLocalSiteOverride = false;
+            if (GlobalSites.Count > 0)
+                SiteUrl = GlobalSites[0].Url;
+        }
+        else if (GlobalSites.Count == 0 || value != GlobalSites[0].Url)
+        {
+            _hasLocalSiteOverride = true;
+        }
+    }
+
     private void ImportCsv()
     {
         var dlg = new OpenFileDialog
@@ -154,6 +175,7 @@ public partial class FolderStructureViewModel : FeatureViewModelBase
     protected override void OnTenantSwitched(TenantProfile profile)
     {
         _currentProfile = profile;
+        _hasLocalSiteOverride = false;
         SiteUrl = string.Empty;
         LibraryTitle = string.Empty;
         PreviewRows = new();

SharepointToolbox/ViewModels/Tabs/SearchViewModel.cs

@@ -19,6 +19,7 @@ public partial class SearchViewModel : FeatureViewModelBase
     private readonly SearchHtmlExportService _htmlExportService;
     private readonly ILogger<FeatureViewModelBase> _logger;
     private TenantProfile? _currentProfile;
+    private bool _hasLocalSiteOverride;
 
     // ── Filter observable properties ─────────────────────────────────────────
 
@@ -73,6 +74,26 @@ public partial class SearchViewModel : FeatureViewModelBase
         ExportHtmlCommand = new AsyncRelayCommand(ExportHtmlAsync, CanExport);
     }
 
+    protected override void OnGlobalSitesChanged(IReadOnlyList<SiteInfo> sites)
+    {
+        if (_hasLocalSiteOverride) return;
+        SiteUrl = sites.Count > 0 ? sites[0].Url : string.Empty;
+    }
+
+    partial void OnSiteUrlChanged(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            _hasLocalSiteOverride = false;
+            if (GlobalSites.Count > 0)
+                SiteUrl = GlobalSites[0].Url;
+        }
+        else if (GlobalSites.Count == 0 || value != GlobalSites[0].Url)
+        {
+            _hasLocalSiteOverride = true;
+        }
+    }
+
     protected override async Task RunOperationAsync(CancellationToken ct, IProgress<OperationProgress> progress)
     {
         if (_currentProfile == null)
@@ -119,6 +140,7 @@ public partial class SearchViewModel : FeatureViewModelBase
     protected override void OnTenantSwitched(Core.Models.TenantProfile profile)
     {
         _currentProfile = profile;
+        _hasLocalSiteOverride = false;
         Results = new ObservableCollection<SearchResult>();
         SiteUrl = string.Empty;
         OnPropertyChanged(nameof(CurrentProfile));

SharepointToolbox/ViewModels/Tabs/StorageViewModel.cs

@@ -19,6 +19,7 @@ public partial class StorageViewModel : FeatureViewModelBase
     private readonly StorageHtmlExportService _htmlExportService;
     private readonly ILogger<FeatureViewModelBase> _logger;
     private TenantProfile? _currentProfile;
+    private bool _hasLocalSiteOverride;
 
     [ObservableProperty]
     private string _siteUrl = string.Empty;
@@ -96,6 +97,26 @@ public partial class StorageViewModel : FeatureViewModelBase
         ExportHtmlCommand = new AsyncRelayCommand(ExportHtmlAsync, CanExport);
     }
 
+    protected override void OnGlobalSitesChanged(IReadOnlyList<SiteInfo> sites)
+    {
+        if (_hasLocalSiteOverride) return;
+        SiteUrl = sites.Count > 0 ? sites[0].Url : string.Empty;
+    }
+
+    partial void OnSiteUrlChanged(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            _hasLocalSiteOverride = false;
+            if (GlobalSites.Count > 0)
+                SiteUrl = GlobalSites[0].Url;
+        }
+        else if (GlobalSites.Count == 0 || value != GlobalSites[0].Url)
+        {
+            _hasLocalSiteOverride = true;
+        }
+    }
+
     protected override async Task RunOperationAsync(CancellationToken ct, IProgress<OperationProgress> progress)
     {
         if (_currentProfile == null)
@@ -147,6 +168,7 @@ public partial class StorageViewModel : FeatureViewModelBase
     protected override void OnTenantSwitched(TenantProfile profile)
     {
         _currentProfile = profile;
+        _hasLocalSiteOverride = false;
         Results = new ObservableCollection<StorageNode>();
         SiteUrl = string.Empty;
         OnPropertyChanged(nameof(CurrentProfile));