refactor: use extensible design for fetching playlist from single file

app/playlistscout.cpp

@@ -0,0 +1,25 @@
+// SPDX-FileCopyrightText: 2026 yyc12345 <yyc12321@outlook.com>
+//
+// SPDX-License-Identifier: MIT
+
+#include "playlistscout.h"
+
+#include "playlistscouts/qtscout.h"
+#include "playlistscouts/explorerscout.h"
+
+std::optional<PlaylistScout::ScoutResult> PlaylistScout::scout(
+    const QUrl &url, const QStringList &allowedSuffixes) {
+
+#ifdef Q_OS_WIN
+    // In Windows, Qt approach can not aware Windows Explorer custom sort order.
+    // So we need to try using Win32 functions for fetching it at first.
+    if (auto rv = PlaylistScout::Explorer::scout(url, allowedSuffixes); rv.has_value()) {
+        return rv;
+    }
+#endif // Q_OS_WIN
+
+    // TODO: We may add macOS Finder, KDE Dolphin and etc supports in future.
+
+    // Qt way is the last fallback.
+    return PlaylistScout::Qt::scout(url, allowedSuffixes);
+}