feat(save): extend GameState to v2 — outfit and held items persisted per character

- Add held_left/held_right fields to CharacterData
- Add get/set_character_outfit and get/set_character_held_item to GameState
- get_save_data now returns version:2 with character_outfits and character_held_items
- apply_save_data resets both dicts when keys absent (empty-dict reset safe)
- 11 new tests in test_game_state.gd — 147/147 passing

scripts/characters/character_data.gd

@@ -11,3 +11,5 @@ enum Species { BUNNY, KITTEN }
 @export var current_floor: int = 0
 @export var position: Vector2 = Vector2.ZERO
 @export var outfit: Array[String] = ["", "", ""]
+@export var held_left: String = ""
+@export var held_right: String = ""