Add ShellDemo sample with comprehensive XAML controls showcase

Complete ShellDemo application demonstrating all MAUI controls:
- App/AppShell: Shell navigation with flyout menu
- HomePage: Feature cards, theme toggle, quick actions
- ButtonsPage: Button styles, states, variations, event logging
- TextInputPage: Entry, Editor, SearchBar with keyboard shortcuts
- SelectionPage: CheckBox, Switch, Slider with colored variants
- PickersPage: Picker, DatePicker, TimePicker demos
- ListsPage: CollectionView with fruits, colors, contacts
- ProgressPage: ProgressBar, ActivityIndicator, interactive demo
- GridsPage: Grid layouts - auto/star/absolute sizing, spans, nesting
- AboutPage: OpenMaui Linux information
- DetailPage: Push/pop navigation demo

All pages use proper XAML with code-behind following MAUI patterns.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

samples/ShellDemo/Pages/PickersPage.xaml.cs

@@ -0,0 +1,92 @@
+using System;
+using Microsoft.Maui.Controls;
+
+namespace ShellDemo.Pages;
+
+public partial class PickersPage : ContentPage
+{
+    private int _eventCount = 0;
+
+    public PickersPage()
+    {
+        InitializeComponent();
+
+        // Set date range for the range picker
+        var startOfMonth = new DateTime(DateTime.Today.Year, DateTime.Today.Month, 1);
+        var endOfMonth = startOfMonth.AddMonths(1).AddDays(-1);
+        RangeDatePicker.MinimumDate = startOfMonth;
+        RangeDatePicker.MaximumDate = endOfMonth;
+    }
+
+    private void LogEvent(string message)
+    {
+        _eventCount++;
+        var timestamp = DateTime.Now.ToString("HH:mm:ss");
+        EventLog.Text = $"[{timestamp}] {_eventCount}. {message}\n{EventLog.Text}";
+    }
+
+    private void OnFruitPickerChanged(object? sender, EventArgs e)
+    {
+        if (FruitPicker.SelectedIndex >= 0)
+        {
+            var item = FruitPicker.ItemsSource[FruitPicker.SelectedIndex]?.ToString();
+            FruitSelectedLabel.Text = $"Selected: {item}";
+            LogEvent($"Fruit selected: {item}");
+        }
+    }
+
+    private void OnColorPickerChanged(object? sender, EventArgs e)
+    {
+        if (ColorPicker.SelectedIndex >= 0)
+        {
+            LogEvent($"Color selected: {ColorPicker.ItemsSource[ColorPicker.SelectedIndex]}");
+        }
+    }
+
+    private void OnSizePickerChanged(object? sender, EventArgs e)
+    {
+        if (sender is Picker picker && picker.SelectedIndex >= 0)
+        {
+            LogEvent($"Size selected: {picker.ItemsSource[picker.SelectedIndex]}");
+        }
+    }
+
+    private void OnDateSelected(object? sender, DateChangedEventArgs e)
+    {
+        DateSelectedLabel.Text = $"Selected: {e.NewDate:d}";
+        LogEvent($"Date selected: {e.NewDate:d}");
+    }
+
+    private void OnRangeDateSelected(object? sender, DateChangedEventArgs e)
+    {
+        LogEvent($"Date (limited): {e.NewDate:d}");
+    }
+
+    private void OnStyledDateSelected(object? sender, DateChangedEventArgs e)
+    {
+        LogEvent($"Styled date: {e.NewDate:d}");
+    }
+
+    private void OnTimeChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
+    {
+        if (e.PropertyName == nameof(TimePicker.Time))
+        {
+            var time = BasicTimePicker.Time;
+            TimeSelectedLabel.Text = $"Selected: {time:hh\\:mm}";
+            LogEvent($"Time selected: {time:hh\\:mm}");
+        }
+    }
+
+    private void OnStyledTimeChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
+    {
+        if (e.PropertyName == nameof(TimePicker.Time) && sender is TimePicker picker)
+        {
+            LogEvent($"Styled time: {picker.Time:hh\\:mm}");
+        }
+    }
+
+    private void OnSetAlarmClicked(object? sender, EventArgs e)
+    {
+        LogEvent($"Alarm set for {AlarmTimePicker.Time:hh\\:mm}");
+    }
+}