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

test/unit/test_game_state.gd

@@ -144,4 +144,40 @@ func test_apply_save_data_restores_held_items() -> void:
 
 func test_save_data_has_version_two() -> void:
 	var data: Dictionary = _state.get_save_data()
-	assert_eq(data.get("version", 0), 2)
+	assert_eq(data.get("version", 0), 3)
+
+
+func test_get_chest_state_returns_empty_for_unknown_id() -> void:
+	assert_eq(GameState.get_chest_state("nonexistent_chest_xyz"), [])
+
+
+func test_set_and_get_chest_state() -> void:
+	GameState.set_chest_state("pharmacy_medicine_test", ["pill_bottle", "syrup"])
+	assert_eq(GameState.get_chest_state("pharmacy_medicine_test"), ["pill_bottle", "syrup"])
+
+
+func test_clear_chest_state_removes_entry() -> void:
+	GameState.set_chest_state("lab_bench_test", ["test_tube"])
+	GameState.clear_chest_state("lab_bench_test")
+	assert_eq(GameState.get_chest_state("lab_bench_test"), [])
+
+
+func test_chest_state_included_in_save_data() -> void:
+	GameState.set_chest_state("xray_cabinet_test", ["xray_sheet"])
+	var data: Dictionary = GameState.get_save_data()
+	assert_true(data.has("chest_states"))
+	assert_eq(data["chest_states"]["xray_cabinet_test"], ["xray_sheet"])
+
+
+func test_save_data_version_is_three() -> void:
+	var data: Dictionary = GameState.get_save_data()
+	assert_eq(data["version"], 3)
+
+
+func test_apply_save_data_restores_chest_state() -> void:
+	var data: Dictionary = {
+		"version": 3,
+		"chest_states": {"reception_desk_test": ["clipboard", "pen"]},
+	}
+	GameState.apply_save_data(data)
+	assert_eq(GameState.get_chest_state("reception_desk_test"), ["clipboard", "pen"])