Add Shorts look preview and visual crop editor

Show opening/closing 9:16 stills from the same filtergraph, and let
users drag a keep-region on a source frame to fill the crop insets.

MainPage.xaml.cs

@@ -1,11 +1,13 @@
 using System.Collections.ObjectModel;
 using System.Diagnostics;
 using System.Globalization;
+using System.Runtime.InteropServices.WindowsRuntime;
 using System.Text;
 using AmiReel.Models;
 using AmiReel.Services;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Media.Imaging;
 using Windows.ApplicationModel.DataTransfer;
 using Windows.Storage;
 using Windows.Storage.Pickers;
@@ -27,6 +29,8 @@ public sealed partial class MainPage : Page
     private bool _keepRenderOutput;
     private List<ShortWizardStep> _wizardSteps = [.. ShortWizard.StepsFor(ShortStyle.Brand)];
     private int _wizardIndex;
+    private int _previewGeneration;
+    private string? _previewDirectory;
 
     public MainPage()
     {
@@ -150,6 +154,8 @@ public sealed partial class MainPage : Page
             ShortSummaryText.Text = BuildShortSummary();
 
         UpdateWizardNavigation();
+        if (IsLoaded && step != ShortWizardStep.Clip)
+            _ = RefreshShortPreviewAsync(automatic: true);
     }
 
     private void UpdateWizardNavigation()
@@ -593,12 +599,126 @@ public sealed partial class MainPage : Page
             ShortFontBox.Text = file.Path;
     }
 
+    private async void OpenCropEditor_Click(object sender, RoutedEventArgs e)
+    {
+        string input = ShortInputBox.Text.Trim();
+        if (string.IsNullOrWhiteSpace(input) || !File.Exists(input))
+        {
+            await ShowMessageAsync("Crop source", "Select a valid source video first.");
+            return;
+        }
+
+        try
+        {
+            CropEditorDialog.XamlRoot = XamlRoot;
+            CropEditorDialog.RequestedTheme = ActualTheme;
+            await ShortCropEditor.LoadVideoFrameAsync(
+                input,
+                string.IsNullOrWhiteSpace(ShortStartBox.Text) ? "00:00:00" : ShortStartBox.Text.Trim(),
+                FfmpegPathBox.Text.Trim(),
+                FfprobePathBox.Text.Trim(),
+                CancellationToken.None);
+            ShortCropEditor.SetInsets(ReadCropInsets());
+
+            ContentDialogResult result = await CropEditorDialog.ShowAsync();
+            if (result != ContentDialogResult.Primary)
+                return;
+
+            PixelInsets insets = ShortCropEditor.Insets;
+            ShortCropLeftBox.Text = insets.Left.ToString(CultureInfo.InvariantCulture);
+            ShortCropRightBox.Text = insets.Right.ToString(CultureInfo.InvariantCulture);
+            ShortCropTopBox.Text = insets.Top.ToString(CultureInfo.InvariantCulture);
+            ShortCropBottomBox.Text = insets.Bottom.ToString(CultureInfo.InvariantCulture);
+        }
+        catch (Exception exception)
+        {
+            await ShowMessageAsync("Crop source", UserFacingErrors.Summarize(exception));
+        }
+    }
+
+    private PixelInsets ReadCropInsets()
+    {
+        static int ReadBox(string text)
+        {
+            return int.TryParse(text, NumberStyles.Integer, CultureInfo.InvariantCulture, out int value) && value > 0
+                ? value
+                : 0;
+        }
+
+        return new PixelInsets(
+            ReadBox(ShortCropLeftBox.Text),
+            ReadBox(ShortCropRightBox.Text),
+            ReadBox(ShortCropTopBox.Text),
+            ReadBox(ShortCropBottomBox.Text));
+    }
+
     private async void PreviewShortSource_Click(object sender, RoutedEventArgs e)
     {
         if (!string.IsNullOrWhiteSpace(ShortInputBox.Text))
             await OpenPreviewAsync(ShortInputBox.Text.Trim());
     }
 
+    private async void UpdateShortPreview_Click(object sender, RoutedEventArgs e) =>
+        await RefreshShortPreviewAsync(automatic: false);
+
+    private async Task RefreshShortPreviewAsync(bool automatic)
+    {
+        if (_isRendering)
+            return;
+
+        int generation = ++_previewGeneration;
+        ShortPreviewProgress.Visibility = Visibility.Visible;
+        UpdateShortPreviewButton.IsEnabled = false;
+        ShortPreviewStatusText.Text = "Rendering 9:16 preview frames...";
+
+        try
+        {
+            ShortSettings settings = ReadShortSettings();
+            ShortsPipeline.ValidatePreview(settings);
+            _previewDirectory ??= Path.Combine(Path.GetTempPath(), "AmiReel", "short-preview", Guid.NewGuid().ToString("N"));
+            Directory.CreateDirectory(_previewDirectory);
+
+            ShortPreviewFrames frames = await new ShortsPipeline().RenderPreviewAsync(
+                settings, _previewDirectory, _ => { }, CancellationToken.None);
+
+            if (generation != _previewGeneration)
+                return;
+
+            ShortPreviewOpeningImage.Source = await LoadPreviewBitmapAsync(frames.OpeningPath);
+            ShortPreviewClosingImage.Source = await LoadPreviewBitmapAsync(frames.ClosingPath);
+            bool hasFont = !string.IsNullOrWhiteSpace(settings.FontFile) && File.Exists(settings.FontFile);
+            ShortPreviewStatusText.Text = hasFont
+                ? $"{settings.Style} · opening hook and closing title card"
+                : "Look only — pick a font on the last step to include the title-card text.";
+        }
+        catch (Exception exception)
+        {
+            if (generation != _previewGeneration)
+                return;
+
+            string message = UserFacingErrors.Summarize(exception);
+            ShortPreviewStatusText.Text = message;
+            if (!automatic)
+                await ShowMessageAsync("Preview failed", message);
+        }
+        finally
+        {
+            if (generation == _previewGeneration)
+            {
+                ShortPreviewProgress.Visibility = Visibility.Collapsed;
+                UpdateShortPreviewButton.IsEnabled = true;
+            }
+        }
+    }
+
+    private static async Task<BitmapImage> LoadPreviewBitmapAsync(string path)
+    {
+        await using FileStream stream = File.OpenRead(path);
+        BitmapImage bitmap = new() { DecodePixelWidth = 296 };
+        await bitmap.SetSourceAsync(stream.AsRandomAccessStream());
+        return bitmap;
+    }
+
     private void SetRendering(bool rendering)
     {
         _isRendering = rendering;