feat: create BulkImportWindow dialog, wire File > Bulk Import

EbayListingTool/Views/BulkImportWindow.xaml

@@ -0,0 +1,11 @@
+<mah:MetroWindow x:Class="EbayListingTool.Views.BulkImportWindow"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:mah="http://metro.mahapps.com/winfx/xaml/controls"
+    xmlns:local="clr-namespace:EbayListingTool.Views"
+    Title="Bulk Import - eBay Listing Tool"
+    Height="700" Width="1000"
+    MinHeight="500" MinWidth="700"
+    WindowStartupLocation="CenterOwner">
+    <local:BulkImportView x:Name="BulkView" />
+</mah:MetroWindow>

EbayListingTool/Views/BulkImportWindow.xaml.cs

@@ -0,0 +1,18 @@
+using EbayListingTool.Services;
+using MahApps.Metro.Controls;
+
+namespace EbayListingTool.Views;
+
+public partial class BulkImportWindow : MetroWindow
+{
+    public BulkImportWindow(
+        EbayListingService listingService,
+        EbayCategoryService categoryService,
+        AiAssistantService aiService,
+        BulkImportService bulkService,
+        EbayAuthService auth)
+    {
+        InitializeComponent();
+        BulkView.Initialise(listingService, categoryService, aiService, bulkService, auth);
+    }
+}

EbayListingTool/Views/MainWindow.xaml.cs

@@ -100,9 +100,15 @@ public partial class MainWindow : MetroWindow
 
     private void BulkImport_Click(object sender, RoutedEventArgs e)
     {
-        // BulkImportWindow is created in Task 7; placeholder for now
-        MessageBox.Show("Bulk Import coming in the next step.", "Bulk Import",
-            MessageBoxButton.OK, MessageBoxImage.Information);
+        if (!_auth.IsConnected)
+        {
+            MessageBox.Show("Please connect to eBay before using Bulk Import.",
+                "Not Connected", MessageBoxButton.OK, MessageBoxImage.Warning);
+            return;
+        }
+        var win = new BulkImportWindow(_listingService, _categoryService, _aiService, _bulkService, _auth);
+        win.Owner = this;
+        win.ShowDialog();
     }
 
     private void Exit_Click(object sender, RoutedEventArgs e) => Close();