refactor: decompose LauncherApp, centralize magic strings/constants, configurable colors

- Extract InputController from AppHost (key handling + ReloadGameEntries)
- Centralize hardcoded values as code constants (non-configurable):
  FavoritesRootName, DefaultFileName, DefaultTitle, scroll fractions,
  AvailableLines helper, removed redundant ArgsTemplate fallback
- Make color scheme configurable via 'Colors' section in launcher.config.json
  with Enum.TryParse + default fallback; MenuRenderer uses constructor injection
- Clean up MenuRenderer: remove dead maxRow logic, unify cache sizing via EnsureCache
- Document intentional error swallowing in FavoritesService.Save/UIErrorService
- Update README + AGENTS.md with configurable color docs
- Remove redundant ArgsTemplate fallback (config is single source of truth)

src/MarcerGameDvdLauncher/AppConfiguration.cs

@@ -4,6 +4,25 @@
 namespace MarcerGameDvdLauncher
 {
     // Configuration POCOs separated into their own file for clarity
+
+    /// <summary>
+    /// Color configuration for the menu renderer.
+    /// All properties have default values matching the original hardcoded scheme,
+    /// so omitting any value (or the entire "Colors" section) preserves existing behaviour.
+    /// </summary>
+    public class AppColorConfig
+    {
+        public ConsoleColor FolderBoth { get; set; } = ConsoleColor.Yellow;
+        public ConsoleColor FolderPatchOnly { get; set; } = ConsoleColor.DarkYellow;
+        public ConsoleColor FolderRootOnly { get; set; } = ConsoleColor.Gray;
+        public ConsoleColor ZipBoth { get; set; } = ConsoleColor.Green;
+        public ConsoleColor ZipRootOnly { get; set; } = ConsoleColor.DarkGreen;
+        public ConsoleColor ZipPatchOnly { get; set; } = ConsoleColor.Magenta;
+        public ConsoleColor SelectedForeground { get; set; } = ConsoleColor.Black;
+        public ConsoleColor SelectedBackground { get; set; } = ConsoleColor.DarkCyan;
+        public ConsoleColor VirtualEntry { get; set; } = ConsoleColor.White;
+    }
+
     public class AppHatariConfig
     {
         public string? Executable { get; set; }
@@ -16,5 +35,9 @@ namespace MarcerGameDvdLauncher
         public string? RootDirectory { get; set; }
         public string? PatchDirectory { get; set; }
         public AppHatariConfig? Hatari { get; set; }
+        // Ignored during JSON deserialization — parsed manually in LoadConfiguration so that
+        // invalid color strings fall back to defaults instead of throwing.
+        [System.Text.Json.Serialization.JsonIgnore]
+        public AppColorConfig? Colors { get; set; }
     }
 }