add reusable options menu plugin with localized UI

- Settings autoloads (Game/Input/Graphics/Audio) backed by FileManager,
  persisted to user:// JSON files
- OptionsMenu scene with tabs wired to each autoload: Game (locale),
  Input (invert vertical axis), Graphics (window mode, borderless,
  screen), Audio (master/music/fx volume)
- GraphicsSettings reads DisplayServer state when running in editor
  to avoid clobbering the editor's window mode; exported builds load
  from disk and apply via set_screen_and_apply with a _loading guard
  to suppress redundant writes
- Built-in translations for en/es/fr/de/ja/zh_CN registered at runtime
  from translations/gd_options.csv
- Control-prompt icon assets for keyboard, PlayStation, Xbox, Nintendo
- Flesh out README with scope and audio bus layout requirement

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugin.gd

@@ -0,0 +1,12 @@
+@tool
+extends EditorPlugin
+
+
+func _enter_tree() -> void:
+	add_autoload_singleton("GameSettings", "res://addons/gd-options/src/common/game_settings.gd")
+	add_autoload_singleton("InputSettings", "res://addons/gd-options/src/common/input_settings.gd")
+	add_autoload_singleton("GraphicsSettings", "res://addons/gd-options/src/common/graphics_settings.gd")
+	add_autoload_singleton("AudioSettings", "res://addons/gd-options/src/common/audio_settings.gd")
+
+func _exit_tree() -> void:
+	pass