feat(01-07): add SettingsView and wire into MainWindow Settings tab

- Create Views/Tabs/SettingsView.xaml (UserControl with language ComboBox en/fr, DataFolder TextBox and Browse button using TranslationSource)
- Create Views/Tabs/SettingsView.xaml.cs (DI constructor injection of SettingsViewModel, LoadAsync on Loaded)
- Update MainWindow.xaml to add xmlns:views namespace and clear placeholder TextBlock from SettingsTabItem
- Register SettingsView as Transient in DI; resolve and set as SettingsTabItem.Content from MainWindow constructor
- All 42 unit tests pass, 0 build errors

SharepointToolbox/MainWindow.xaml

@@ -5,6 +5,7 @@
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
         xmlns:loc="clr-namespace:SharepointToolbox.Localization"
         xmlns:controls="clr-namespace:SharepointToolbox.Views.Controls"
+        xmlns:views="clr-namespace:SharepointToolbox.Views.Tabs"
         mc:Ignorable="d"
         Title="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[app.title]}"
         MinWidth="900" MinHeight="600" Height="700" Width="1100">
@@ -61,10 +62,9 @@
       <TabItem Header="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[tab.structure]}">
         <controls:FeatureTabBase />
       </TabItem>
-      <!-- Settings tab: placeholder TextBlock replaced by SettingsView in plan 01-07 -->
+      <!-- Settings tab: content set from code-behind via DI-resolved SettingsView -->
       <TabItem x:Name="SettingsTabItem"
                Header="{Binding Source={x:Static loc:TranslationSource.Instance}, Path=[tab.settings]}">
-        <TextBlock Text="Settings (plan 01-07)" HorizontalAlignment="Center" VerticalAlignment="Center" />
       </TabItem>
     </TabControl>
   </DockPanel>