feat(items): add chest-return priority to HoldableItem and GameState v3 chest states

- HoldableItem._try_return_to_chest() snaps item back if within CHEST_RETURN_RADIUS (80px)
- _on_drag_released checks chest return before hand-slot fallback
- OutfitItem._on_drag_released checks chest return before outfit/hand-slot logic
- GameState: _chest_states dict + get/set/clear_chest_state methods
- GameState.get_save_data() bumped to version 3, includes chest_states
- GameState.apply_save_data() restores chest_states from save data

scripts/autoload/GameState.gd

@@ -8,6 +8,7 @@ var _character_positions: Dictionary = {}
 var _character_outfits: Dictionary = {}
 var _character_held_items: Dictionary = {}
 var _object_states: Dictionary = {}
+var _chest_states: Dictionary = {}
 var current_room: String = "reception"
 var music_volume: float = 0.6
 var sfx_volume: float = 1.0
@@ -58,17 +59,32 @@ func set_object_state(id: String, state: String) -> void:
 	state_changed.emit()
 
 
+func get_chest_state(chest_id: String) -> Array:
+	return _chest_states.get(chest_id, [])
+
+
+func set_chest_state(chest_id: String, spawned_item_ids: Array) -> void:
+	_chest_states[chest_id] = spawned_item_ids
+	state_changed.emit()
+
+
+func clear_chest_state(chest_id: String) -> void:
+	_chest_states.erase(chest_id)
+	state_changed.emit()
+
+
 func get_save_data() -> Dictionary:
 	var positions: Dictionary = {}
 	for key: String in _character_positions:
 		var pos: Vector2 = _character_positions[key]
 		positions[key] = [pos.x, pos.y]
 	return {
-		"version": 2,
+		"version": 3,
 		"character_positions": positions,
 		"character_outfits": _character_outfits.duplicate(true),
 		"character_held_items": _character_held_items.duplicate(true),
 		"object_states": _object_states,
+		"chest_states": _chest_states.duplicate(true),
 		"current_room": current_room,
 		"music_volume": music_volume,
 		"sfx_volume": sfx_volume,
@@ -98,3 +114,7 @@ func apply_save_data(data: Dictionary) -> void:
 		music_volume = data["music_volume"]
 	if data.has("sfx_volume"):
 		sfx_volume = data["sfx_volume"]
+	if data.has("chest_states"):
+		_chest_states = data["chest_states"].duplicate(true)
+	else:
+		_chest_states = {}