Add adaptive layout for foldable devices

Replace static Phone/Tablet view selection with AdaptiveMainView
that listens to OnSizeChanged and dynamically swaps between
PhoneMainView (<600px) and TabletMainView (>=600px). This handles
foldable device fold/unfold and rotation at runtime.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: sharpninja

src/RequestTracker.Android/App.axaml.cs

@@ -36,9 +36,7 @@ public override void OnFrameworkInitializationCompleted()
                     {
                         var clipboardService = new AndroidClipboardService();
                         var vm = new MainWindowViewModel(clipboardService, mcpBaseUrl);
-                        singleView.MainView = DeviceFormFactor.IsTablet()
-                            ? new TabletMainView { DataContext = vm }
-                            : (Control)new PhoneMainView { DataContext = vm };
+                        singleView.MainView = new AdaptiveMainView { DataContext = vm };
                         vm.InitializeAfterWindowShown();
                     }
                     catch (Exception ex)

src/RequestTracker.Android/Views/AdaptiveMainView.axaml

@@ -0,0 +1,14 @@
+<UserControl xmlns="https://github.com/avaloniaui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:vm="using:RequestTracker.Core.ViewModels"
+             xmlns:views="using:RequestTracker.Android.Views"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d"
+             x:Class="RequestTracker.Android.Views.AdaptiveMainView"
+             x:DataType="vm:MainWindowViewModel">
+
+    <Panel x:Name="HostPanel">
+        <!-- Content is set dynamically in code-behind based on available width -->
+    </Panel>
+</UserControl>

src/RequestTracker.Android/Views/AdaptiveMainView.axaml.cs

@@ -0,0 +1,61 @@
+using System;
+using Avalonia;
+using Avalonia.Controls;
+using Avalonia.Markup.Xaml;
+
+namespace RequestTracker.Android.Views;
+
+/// <summary>
+/// Switches between PhoneMainView and TabletMainView based on available width.
+/// Reacts to fold/unfold and rotation on foldable devices.
+/// </summary>
+public partial class AdaptiveMainView : UserControl
+{
+    private const double TabletWidthThreshold = 600;
+    private bool _isTabletLayout;
+    private Control? _currentView;
+    private Panel? _hostPanel;
+
+    public AdaptiveMainView()
+    {
+        InitializeComponent();
+        _hostPanel = this.FindControl<Panel>("HostPanel");
+    }
+
+    protected override void OnSizeChanged(SizeChangedEventArgs e)
+    {
+        base.OnSizeChanged(e);
+        UpdateLayout(e.NewSize.Width);
+    }
+
+    protected override void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
+    {
+        base.OnAttachedToVisualTree(e);
+        UpdateLayout(Bounds.Width);
+    }
+
+    private void UpdateLayout(double availableWidth)
+    {
+        bool shouldBeTablet = availableWidth >= TabletWidthThreshold;
+
+        if (_currentView != null && shouldBeTablet == _isTabletLayout)
+            return;
+
+        _isTabletLayout = shouldBeTablet;
+        var dc = DataContext;
+
+        Control newView = shouldBeTablet
+            ? new TabletMainView()
+            : new PhoneMainView();
+
+        newView.DataContext = dc;
+
+        if (_hostPanel != null)
+        {
+            _hostPanel.Children.Clear();
+            _hostPanel.Children.Add(newView);
+        }
+
+        _currentView = newView;
+    }
+}