feat(configmanager): add IDialogService interface and AvaloniaDialogService

Add dialog service abstraction for platform-specific dialogs:
- IDialogService interface with folder picker, message, confirmation,
  diff preview, and validation results methods
- AvaloniaDialogService implementation using MsBox.Avalonia
- Basic implementations for ShowDiffPreviewAsync and ShowValidationResultsAsync
  (full dialogs to be implemented in Tasks 22-23)
- Add MessageBox.Avalonia package reference

NEW/src/Utils/JdeScoping.ConfigManager/JdeScoping.ConfigManager.csproj

@@ -17,6 +17,7 @@
     <PackageReference Include="Avalonia.Fonts.Inter" Version="11.2.*" />
     <PackageReference Include="Avalonia.Diagnostics" Version="11.2.*" Condition="'$(Configuration)' == 'Debug'" />
     <PackageReference Include="DiffPlex" Version="1.7.*" />
+    <PackageReference Include="MessageBox.Avalonia" Version="3.1.*" />
     <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="9.0.*" />
     <PackageReference Include="Microsoft.Extensions.Logging" Version="9.0.*" />
     <PackageReference Include="Microsoft.Extensions.Logging.Console" Version="9.0.*" />

NEW/src/Utils/JdeScoping.ConfigManager/Services/AvaloniaDialogService.cs

@@ -0,0 +1,149 @@
+using System.Text;
+using Avalonia.Controls;
+using Avalonia.Platform.Storage;
+using MsBox.Avalonia;
+using MsBox.Avalonia.Enums;
+
+namespace JdeScoping.ConfigManager.Services;
+
+/// <summary>
+/// Avalonia implementation of IDialogService using MsBox.Avalonia and platform storage.
+/// </summary>
+public class AvaloniaDialogService : IDialogService
+{
+    private readonly Func<Window?> _getMainWindow;
+
+    /// <summary>
+    /// Creates a new instance of AvaloniaDialogService.
+    /// </summary>
+    /// <param name="getMainWindow">Factory function to get the main window for dialogs.</param>
+    public AvaloniaDialogService(Func<Window?> getMainWindow)
+    {
+        _getMainWindow = getMainWindow ?? throw new ArgumentNullException(nameof(getMainWindow));
+    }
+
+    /// <inheritdoc />
+    public async Task<string?> ShowFolderPickerAsync(string? title = null)
+    {
+        var window = _getMainWindow();
+        if (window == null)
+            return null;
+
+        var folders = await window.StorageProvider.OpenFolderPickerAsync(new FolderPickerOpenOptions
+        {
+            Title = title ?? "Select Folder",
+            AllowMultiple = false
+        });
+
+        return folders.Count > 0 ? folders[0].Path.LocalPath : null;
+    }
+
+    /// <inheritdoc />
+    public async Task ShowMessageAsync(string title, string message)
+    {
+        var box = MessageBoxManager.GetMessageBoxStandard(title, message, ButtonEnum.Ok, Icon.Info);
+        var window = _getMainWindow();
+        if (window != null)
+        {
+            await box.ShowWindowDialogAsync(window);
+        }
+        else
+        {
+            await box.ShowAsync();
+        }
+    }
+
+    /// <inheritdoc />
+    public async Task<bool> ShowConfirmationAsync(string title, string message)
+    {
+        var box = MessageBoxManager.GetMessageBoxStandard(title, message, ButtonEnum.YesNo, Icon.Question);
+        var window = _getMainWindow();
+        ButtonResult result;
+        if (window != null)
+        {
+            result = await box.ShowWindowDialogAsync(window);
+        }
+        else
+        {
+            result = await box.ShowAsync();
+        }
+        return result == ButtonResult.Yes;
+    }
+
+    /// <inheritdoc />
+    public async Task<bool> ShowDiffPreviewAsync(string title, DiffResult diff)
+    {
+        // Basic implementation - full diff preview dialog will be implemented in Task 22
+        if (!diff.HasChanges)
+        {
+            await ShowMessageAsync(title, "No changes detected.");
+            return false;
+        }
+
+        var summary = new StringBuilder();
+        summary.AppendLine($"Changes detected: {diff.Insertions} insertion(s), {diff.Deletions} deletion(s)");
+        summary.AppendLine();
+        summary.AppendLine("Do you want to apply these changes?");
+
+        return await ShowConfirmationAsync(title, summary.ToString());
+    }
+
+    /// <inheritdoc />
+    public async Task ShowValidationResultsAsync(ValidationResult appSettingsResult, ValidationResult pipelinesResult)
+    {
+        // Basic implementation - full validation results dialog will be implemented in Task 23
+        var message = new StringBuilder();
+
+        message.AppendLine("=== AppSettings Validation ===");
+        if (appSettingsResult.IsValid)
+        {
+            message.AppendLine("Valid");
+        }
+        else
+        {
+            foreach (var error in appSettingsResult.Errors)
+            {
+                message.AppendLine($"Error: {error}");
+            }
+        }
+        foreach (var warning in appSettingsResult.Warnings)
+        {
+            message.AppendLine($"Warning: {warning}");
+        }
+
+        message.AppendLine();
+        message.AppendLine("=== Pipelines Validation ===");
+        if (pipelinesResult.IsValid)
+        {
+            message.AppendLine("Valid");
+        }
+        else
+        {
+            foreach (var error in pipelinesResult.Errors)
+            {
+                message.AppendLine($"Error: {error}");
+            }
+        }
+        foreach (var warning in pipelinesResult.Warnings)
+        {
+            message.AppendLine($"Warning: {warning}");
+        }
+
+        var title = appSettingsResult.IsValid && pipelinesResult.IsValid
+            ? "Validation Passed"
+            : "Validation Issues Found";
+
+        var icon = appSettingsResult.IsValid && pipelinesResult.IsValid ? Icon.Success : Icon.Warning;
+
+        var box = MessageBoxManager.GetMessageBoxStandard(title, message.ToString(), ButtonEnum.Ok, icon);
+        var window = _getMainWindow();
+        if (window != null)
+        {
+            await box.ShowWindowDialogAsync(window);
+        }
+        else
+        {
+            await box.ShowAsync();
+        }
+    }
+}

NEW/src/Utils/JdeScoping.ConfigManager/Services/IDialogService.cs

@@ -0,0 +1,45 @@
+namespace JdeScoping.ConfigManager.Services;
+
+/// <summary>
+/// Abstraction for platform-specific dialog operations.
+/// Enables unit testing of view models that need to show dialogs.
+/// </summary>
+public interface IDialogService
+{
+    /// <summary>
+    /// Shows a folder picker dialog.
+    /// </summary>
+    /// <param name="title">Optional title for the dialog.</param>
+    /// <returns>The selected folder path, or null if cancelled.</returns>
+    Task<string?> ShowFolderPickerAsync(string? title = null);
+
+    /// <summary>
+    /// Shows a message dialog.
+    /// </summary>
+    /// <param name="title">The dialog title.</param>
+    /// <param name="message">The message to display.</param>
+    Task ShowMessageAsync(string title, string message);
+
+    /// <summary>
+    /// Shows a confirmation dialog with Yes/No options.
+    /// </summary>
+    /// <param name="title">The dialog title.</param>
+    /// <param name="message">The confirmation message to display.</param>
+    /// <returns>True if user clicked Yes, false otherwise.</returns>
+    Task<bool> ShowConfirmationAsync(string title, string message);
+
+    /// <summary>
+    /// Shows a diff preview dialog allowing the user to review changes.
+    /// </summary>
+    /// <param name="title">The dialog title.</param>
+    /// <param name="diff">The diff result to display.</param>
+    /// <returns>True if user confirms the changes, false otherwise.</returns>
+    Task<bool> ShowDiffPreviewAsync(string title, DiffResult diff);
+
+    /// <summary>
+    /// Shows validation results for configuration files.
+    /// </summary>
+    /// <param name="appSettingsResult">Validation result for appsettings.json.</param>
+    /// <param name="pipelinesResult">Validation result for pipelines.json.</param>
+    Task ShowValidationResultsAsync(ValidationResult appSettingsResult, ValidationResult pipelinesResult);
+}