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/launcher.config.example.json

@@ -5,5 +5,16 @@
     "Executable": "C:\\Tools\\hatari\\hatari.exe",
     "ConfigFile": "C:\\Tools\\hatari\\hatari-st.cfg",
     "ArgsTemplate": "-c \"{cfg}\" --disk-a \"{zip}\""
+  },
+  "Colors": {
+    "FolderBoth": "Yellow",
+    "FolderPatchOnly": "DarkYellow",
+    "FolderRootOnly": "Gray",
+    "ZipBoth": "Green",
+    "ZipRootOnly": "DarkGreen",
+    "ZipPatchOnly": "Magenta",
+    "SelectedForeground": "Black",
+    "SelectedBackground": "DarkCyan",
+    "VirtualEntry": "White"
   }
 }