feat(core): implement room navigation, character states, save/load and settings menu

- RoomNavigator autoload: smooth camera pan between floors
- Floor1 and Floor2 placeholder rooms with elevator buttons
- CharacterData Resource with State enum (HEALTHY/SICK/SLEEPING/TIRED)
- Character visual state feedback via ColorRect color
- Main scene loads saved state on startup
- SettingsMenu with music/sfx sliders and game reset
- HUD settings button to open SettingsMenu

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/objects/elevator_button.gd

@@ -0,0 +1,30 @@
+## ElevatorButton — tappable button that navigates the camera to a target floor.
+class_name ElevatorButton extends Node2D
+
+@export var target_floor: int = 0
+
+var _area: Area2D
+
+
+func _ready() -> void:
+	_area = get_node_or_null("CollisionArea") as Area2D
+	if _area != null:
+		_area.input_event.connect(_on_input_event)
+
+
+func _on_input_event(_viewport: Node, event: InputEvent, _shape_idx: int) -> void:
+	if event is InputEventMouseButton and event.pressed and event.button_index == MOUSE_BUTTON_LEFT:
+		_on_pressed()
+	elif event is InputEventScreenTouch and event.pressed:
+		_on_pressed()
+
+
+func _on_pressed() -> void:
+	RoomNavigator.go_to_floor(target_floor)
+	_play_bounce()
+
+
+func _play_bounce() -> void:
+	var tween: Tween = create_tween()
+	tween.tween_property(self, "scale", Vector2(1.15, 1.15), 0.08)
+	tween.tween_property(self, "scale", Vector2(1.0, 1.0), 0.08)