Baseline: WPF/Avalonia/Cli/Core + plans (BROWSER_FEATURES_PLAN v2, MOBILE_PLAN v1)

VideoDownloader.App/Core/ConfigStore.cs

@@ -0,0 +1,35 @@
+using System.Text.Json;
+using VideoDownloader.Core.Config;
+
+namespace VideoDownloader.App.Core;
+
+/// <summary>%AppData%/VideoDownloader/config.json 으로 설정 영속화</summary>
+public static class ConfigStore
+{
+    private static string Dir => Path.Combine(
+        Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData), "VideoDownloader");
+    private static string FilePath => Path.Combine(Dir, "config.json");
+
+    private static readonly JsonSerializerOptions JsonOpts = new() { WriteIndented = true };
+
+    public static AppConfig Load()
+    {
+        try
+        {
+            if (File.Exists(FilePath))
+                return JsonSerializer.Deserialize<AppConfig>(File.ReadAllText(FilePath)) ?? new AppConfig();
+        }
+        catch { /* 손상 시 기본값 */ }
+        return new AppConfig();
+    }
+
+    public static void Save(AppConfig config)
+    {
+        try
+        {
+            Directory.CreateDirectory(Dir);
+            File.WriteAllText(FilePath, JsonSerializer.Serialize(config, JsonOpts));
+        }
+        catch { /* 저장 실패는 무시 */ }
+    }
+}