Make Windows navigation functional

src/ServerMonitorManager.Desktop/MainPage.xaml

@@ -101,6 +101,7 @@
                 Severity="Informational" />
 
             <Border
+                x:Name="OverviewSummary"
                 Grid.Row="2"
                 Margin="0,24,0,0"
                 Padding="20,18"
@@ -145,7 +146,7 @@
                 </Grid>
             </Border>
 
-            <ScrollViewer Grid.Row="3" Margin="0,28,0,0">
+            <ScrollViewer x:Name="WorkspaceScroll" Grid.Row="3" Margin="0,28,0,0">
                 <Grid x:Name="WorkspaceGrid" ColumnSpacing="24" RowSpacing="24">
                     <Grid.ColumnDefinitions>
                         <ColumnDefinition Width="*" />
@@ -341,6 +342,23 @@
                     </VisualStateManager.VisualStateGroups>
                 </Grid>
             </ScrollViewer>
+
+            <StackPanel
+                x:Name="NavigationPlaceholder"
+                Grid.Row="3"
+                Margin="0,36,0,0"
+                HorizontalAlignment="Center"
+                VerticalAlignment="Top"
+                MaxWidth="560"
+                Spacing="12"
+                Visibility="Collapsed">
+                <TextBlock x:Name="PlaceholderTitle" HorizontalAlignment="Center" Style="{StaticResource TitleTextBlockStyle}" />
+                <TextBlock
+                    x:Name="PlaceholderDescription"
+                    Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                    TextAlignment="Center"
+                    TextWrapping="Wrap" />
+            </StackPanel>
         </Grid>
     </NavigationView>
 </Page>

src/ServerMonitorManager.Desktop/MainPage.xaml.cs

@@ -539,10 +539,57 @@ public sealed partial class MainPage : Page
     {
         if (args.IsSettingsSelected)
         {
-            ShowInfo(
+            ShowPlaceholder(
                 "Настройки",
-                "Профили серверов хранятся локально; приватный SSH-ключ не покидает этот ПК.",
+                "Профили серверов хранятся локально. Настройки ключей, интервалов обновления и подтверждений будут добавляться здесь.");
-                InfoBarSeverity.Informational);
+            return;
+        }
+
+        var tag = (args.SelectedItem as NavigationViewItem)?.Tag?.ToString() ?? "overview";
+        NavigationPlaceholder.Visibility = Visibility.Collapsed;
+        OverviewSummary.Visibility = Visibility.Visible;
+        WorkspaceScroll.Visibility = Visibility.Visible;
+        ServerWorkspace.Visibility = tag is "overview" or "servers" ? Visibility.Visible : Visibility.Collapsed;
+        LinkInspector.Visibility = tag is "overview" or "links" ? Visibility.Visible : Visibility.Collapsed;
+        InspectorColumn.Width = tag == "overview" && ActualWidth >= 1080
+            ? new GridLength(360)
+            : new GridLength(0);
+
+        if (tag == "links")
+        {
+            Grid.SetRow(LinkInspector, 0);
+            Grid.SetColumn(LinkInspector, 0);
+            Grid.SetColumnSpan(LinkInspector, 2);
+        }
+        else
+        {
+            Grid.SetColumnSpan(LinkInspector, 1);
+            if (ActualWidth >= 1080)
+            {
+                Grid.SetRow(LinkInspector, 0);
+                Grid.SetColumn(LinkInspector, 1);
+            }
+            else
+            {
+                Grid.SetRow(LinkInspector, 1);
+                Grid.SetColumn(LinkInspector, 0);
+            }
+        }
+
+        if (tag == "sessions")
+        {
+            ShowPlaceholder(
+                "SSH-сессии",
+                "Интерактивные терминалы будут использовать отдельную identity и не получат ключ мониторинга или права Mesh Hub.");
         }
     }
+
+    private void ShowPlaceholder(string title, string description)
+    {
+        OverviewSummary.Visibility = Visibility.Collapsed;
+        WorkspaceScroll.Visibility = Visibility.Collapsed;
+        PlaceholderTitle.Text = title;
+        PlaceholderDescription.Text = description;
+        NavigationPlaceholder.Visibility = Visibility.Visible;
+    }
 }