refactor(3): VideoDownloader.Browser library - tabs/find/search-engine/zoom/bookmark-history stores extracted from App (66 GREEN)

VideoDownloader.Core/Platform/CorePaths.cs

@@ -0,0 +1,13 @@
+namespace VideoDownloader.Core.Platform;
+
+/// <summary>
+/// 앱 데이터 디렉터리 결정(Core 레벨). 기본 %AppData%/VideoDownloader.
+/// VD_DATA_DIR 환경변수로 오버라이드 — E2E 테스트 격리 공식 후크.
+/// </summary>
+public static class CorePaths
+{
+    public static string DataDir =>
+        Environment.GetEnvironmentVariable("VD_DATA_DIR") is { Length: > 0 } env
+            ? env
+            : Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "VideoDownloader");
+}