refactor(1): detection App->Core + AppPaths (VD_DATA_DIR isolation for deterministic E2E)

VideoDownloader.App/MainWindow.xaml.cs

@@ -145,9 +145,8 @@ public partial class MainWindow : Window
     [DllImport("dwmapi.dll")]
     private static extern int DwmSetWindowAttribute(IntPtr hwnd, int attribute, ref int pvAttribute, int cbAttribute);
 
-    /// <summary>WebView2 영속 프로필 경로. 쿠키·세션·localStorage·캐시가 여기 보존되어 앱/빌드 재시작에도 유지.</summary>
-    internal static string AppDataDir => Path.Combine(
-        Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "VideoDownloader");
+    /// <summary>앱 데이터 디렉터리(AppPaths.DataDir — VD_DATA_DIR 오버라이드 지원).</summary>
+    internal static string AppDataDir => AppPaths.DataDir;
 
     internal static string ProfileFolder => Path.Combine(AppDataDir, "webview");