feat(configmanager): wire up form selection in MainWindowViewModel

- Add IFileSystem and IDialogService dependencies to constructor
- Implement OnSelectedNodeChanged to create appropriate form ViewModels
- Add LoadConfigForTesting helper for unit testing
- Add MarkAsChanged helper to track unsaved changes
- Update OpenFolderAsync to use IDialogService
- Add comprehensive unit tests for form selection

NEW/src/Utils/JdeScoping.ConfigManager/ViewModels/MainWindowViewModel.cs

@@ -3,6 +3,7 @@ using System.Windows.Input;
 using Avalonia.Media;
 using JdeScoping.ConfigManager.Models;
 using JdeScoping.ConfigManager.Services;
+using JdeScoping.ConfigManager.ViewModels.Forms;
 using Microsoft.Extensions.Logging;
 
 namespace JdeScoping.ConfigManager.ViewModels;
@@ -12,10 +13,12 @@ namespace JdeScoping.ConfigManager.ViewModels;
 /// </summary>
 public class MainWindowViewModel : ViewModelBase
 {
+    private readonly IFileSystem _fileSystem;
     private readonly IConfigFileService _configFileService;
     private readonly IValidationService _validationService;
     private readonly IBackupService _backupService;
     private readonly IAutoDiscoveryService _autoDiscoveryService;
+    private readonly IDialogService? _dialogService;
     private readonly ILogger<MainWindowViewModel>? _logger;
 
     private string _configFolderPath = "No folder selected";
@@ -28,30 +31,45 @@ public class MainWindowViewModel : ViewModelBase
     private ConfigModel? _appSettings;
     private PipelinesConfigModel? _pipelines;
 
+    /// <summary>
+    /// Gets or sets the currently loaded configuration folder path.
+    /// </summary>
     public string ConfigFolderPath
     {
         get => _configFolderPath;
         set => SetProperty(ref _configFolderPath, value);
     }
 
+    /// <summary>
+    /// Gets or sets a value indicating whether there are unsaved configuration changes.
+    /// </summary>
     public bool HasUnsavedChanges
     {
         get => _hasUnsavedChanges;
         set => SetProperty(ref _hasUnsavedChanges, value);
     }
 
+    /// <summary>
+    /// Gets or sets the validation status message displayed to the user.
+    /// </summary>
     public string ValidationStatus
     {
         get => _validationStatus;
         set => SetProperty(ref _validationStatus, value);
     }
 
+    /// <summary>
+    /// Gets or sets the brush color for the validation status indicator.
+    /// </summary>
     public IBrush ValidationStatusColor
     {
         get => _validationStatusColor;
         set => SetProperty(ref _validationStatusColor, value);
     }
 
+    /// <summary>
+    /// Gets or sets the currently selected tree node in the configuration tree view.
+    /// </summary>
     public TreeNodeViewModel? SelectedNode
     {
         get => _selectedNode;
@@ -62,33 +80,80 @@ public class MainWindowViewModel : ViewModelBase
         }
     }
 
+    /// <summary>
+    /// Gets or sets the view model for the form displayed when a node is selected.
+    /// </summary>
     public object? SelectedFormViewModel
     {
         get => _selectedFormViewModel;
         set => SetProperty(ref _selectedFormViewModel, value);
     }
 
+    /// <summary>
+    /// Gets the collection of tree nodes representing the configuration structure.
+    /// </summary>
     public ObservableCollection<TreeNodeViewModel> TreeNodes { get; } = [];
 
+    /// <summary>
+    /// Gets the command for opening a configuration folder.
+    /// </summary>
     public ICommand OpenFolderCommand { get; }
+
+    /// <summary>
+    /// Gets the command for saving configuration changes.
+    /// </summary>
     public ICommand SaveCommand { get; }
+
+    /// <summary>
+    /// Gets the command for exiting the application.
+    /// </summary>
     public ICommand ExitCommand { get; }
+
+    /// <summary>
+    /// Gets the command for undoing the last configuration change.
+    /// </summary>
     public ICommand UndoCommand { get; }
+
+    /// <summary>
+    /// Gets the command for redoing the last undone configuration change.
+    /// </summary>
     public ICommand RedoCommand { get; }
+
+    /// <summary>
+    /// Gets the command for validating the current configuration.
+    /// </summary>
     public ICommand ValidateCommand { get; }
+
+    /// <summary>
+    /// Gets the command for testing database connections.
+    /// </summary>
     public ICommand TestConnectionCommand { get; }
 
+    /// <summary>
+    /// Initializes a new instance of the <see cref="MainWindowViewModel"/> class.
+    /// </summary>
+    /// <param name="fileSystem">File system abstraction for I/O operations.</param>
+    /// <param name="configFileService">Service for loading and saving configuration files.</param>
+    /// <param name="validationService">Service for validating configuration settings.</param>
+    /// <param name="backupService">Service for creating configuration backups.</param>
+    /// <param name="autoDiscoveryService">Service for discovering configuration folder locations.</param>
+    /// <param name="dialogService">Service for showing platform dialogs.</param>
+    /// <param name="logger">Optional logger for recording view model activities.</param>
     public MainWindowViewModel(
+        IFileSystem fileSystem,
         IConfigFileService configFileService,
         IValidationService validationService,
         IBackupService backupService,
         IAutoDiscoveryService autoDiscoveryService,
+        IDialogService? dialogService,
         ILogger<MainWindowViewModel>? logger)
     {
+        _fileSystem = fileSystem;
         _configFileService = configFileService;
         _validationService = validationService;
         _backupService = backupService;
         _autoDiscoveryService = autoDiscoveryService;
+        _dialogService = dialogService;
         _logger = logger;
 
         OpenFolderCommand = new AsyncRelayCommand(OpenFolderAsync);
@@ -106,10 +171,12 @@ public class MainWindowViewModel : ViewModelBase
     /// Design-time constructor for XAML previewer.
     /// </summary>
     public MainWindowViewModel() : this(
+        new FileSystem(),
         new ConfigFileService(new FileSystem()),
         new ValidationService(),
         new BackupService(new FileSystem()),
         new AutoDiscoveryService(new FileSystem()),
+        null,
         null)
     {
     }
@@ -131,9 +198,17 @@ public class MainWindowViewModel : ViewModelBase
     /// </summary>
     private async Task OpenFolderAsync()
     {
-        // TODO: Show folder picker dialog
-        _logger?.LogInformation("Open folder requested");
-        await Task.CompletedTask;
+        if (_dialogService == null)
+        {
+            _logger?.LogWarning("Dialog service is not available");
+            return;
+        }
+
+        var folder = await _dialogService.ShowFolderPickerAsync("Select Configuration Folder");
+        if (folder != null)
+        {
+            await LoadConfigAsync(folder);
+        }
     }
 
     /// <summary>
@@ -201,8 +276,48 @@ public class MainWindowViewModel : ViewModelBase
     /// </summary>
     private void OnSelectedNodeChanged()
     {
-        // TODO: Load appropriate form ViewModel based on selected node
-        SelectedFormViewModel = null;
+        if (_selectedNode == null || _appSettings == null)
+        {
+            SelectedFormViewModel = null;
+            return;
+        }
+
+        SelectedFormViewModel = _selectedNode.SectionKey switch
+        {
+            "DataSync" => new DataSyncFormViewModel(_appSettings.DataSync, MarkAsChanged),
+            "DataAccess" => new DataAccessFormViewModel(_appSettings.DataAccess, MarkAsChanged),
+            "Auth" => new AuthFormViewModel(_appSettings.Auth, MarkAsChanged),
+            "Ldap" => new LdapFormViewModel(_appSettings.Ldap, MarkAsChanged),
+            "Search" => new SearchFormViewModel(_appSettings.Search, MarkAsChanged),
+            "ExcelExport" => new ExcelExportFormViewModel(_appSettings.ExcelExport, MarkAsChanged),
+            _ when _selectedNode.NodeType == TreeNodeType.Pipeline && _pipelines != null
+                => _pipelines.Pipelines.TryGetValue(_selectedNode.SectionKey!, out var pipeline)
+                    ? new PipelineFormViewModel(_selectedNode.SectionKey!, pipeline, MarkAsChanged)
+                    : null,
+            _ => null
+        };
+    }
+
+    /// <summary>
+    /// Marks the configuration as having unsaved changes.
+    /// </summary>
+    private void MarkAsChanged()
+    {
+        HasUnsavedChanges = true;
+        if (_selectedNode != null)
+            _selectedNode.IsModified = true;
+    }
+
+    /// <summary>
+    /// Loads configuration for testing purposes.
+    /// </summary>
+    /// <param name="appSettings">The application settings configuration model.</param>
+    /// <param name="pipelines">The pipelines configuration model.</param>
+    public void LoadConfigForTesting(ConfigModel? appSettings, PipelinesConfigModel? pipelines)
+    {
+        _appSettings = appSettings;
+        _pipelines = pipelines;
+        BuildTreeNodes();
     }
 
     /// <summary>