Fix missing taskbar/Alt+Tab icon

AppWindow.SetIcon(executablePath) was passing the .exe's own path, but that
API requires an actual .ico file path — passing an .exe silently does
nothing, so the window fell back to a generic placeholder icon in the
taskbar and Alt+Tab (the custom title bar icon fixed earlier is a separate,
XAML-drawn Image and was unaffected).

Embed branding/AmiReel.ico as a resource, extract it once to
%LOCALAPPDATA%\AmiReel\app-icon.ico on startup, and call
AppWindow.SetIcon() with that file path instead. Verified via WM_GETICON
against the running window's HWND that both the big and small icons now
resolve to the real AmiReel logo.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

MainWindow.xaml.cs

@@ -34,10 +34,7 @@ public sealed partial class MainWindow : Window
         ExtendsContentIntoTitleBar = true;
         SetTitleBar(AppTitleBar);
 
-        string? executablePath = Environment.ProcessPath;
-        if (!string.IsNullOrWhiteSpace(executablePath) && File.Exists(executablePath))
-            AppWindow.SetIcon(executablePath);
-
+        SetWindowIcon();
         SetDefaultSizeAndPosition();
         LoadTitleBarIcon();
 
@@ -47,6 +44,38 @@ public sealed partial class MainWindow : Window
         AppWindow.Closing += AppWindow_Closing;
     }
 
+    /// <summary>
+    /// Sets the window's taskbar/Alt+Tab icon. <see cref="AppWindow.SetIcon(string)"/> requires an
+    /// actual .ico file path (an .exe path is silently ignored), so the embedded .ico is extracted
+    /// once to a stable file under %LOCALAPPDATA% and that path is used instead.
+    /// </summary>
+    private void SetWindowIcon()
+    {
+        try
+        {
+            string iconPath = Path.Combine(
+                Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+                "AmiReel", "app-icon.ico");
+
+            if (!File.Exists(iconPath))
+            {
+                Directory.CreateDirectory(Path.GetDirectoryName(iconPath)!);
+                Assembly assembly = Assembly.GetExecutingAssembly();
+                using Stream? resource = assembly.GetManifestResourceStream("AmiReel.Assets.AppIcon.ico");
+                if (resource is null) return;
+
+                using FileStream file = File.Create(iconPath);
+                resource.CopyTo(file);
+            }
+
+            AppWindow.SetIcon(iconPath);
+        }
+        catch
+        {
+            // Non-critical: the window simply keeps whatever default icon Windows assigned.
+        }
+    }
+
     /// <summary>
     /// Loads the title bar icon from an embedded resource instead of an "ms-appx:///Assets/..."
     /// URI. A single-file self-contained publish bundles Content/Assets items into the exe in a