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/systems/room_navigator.gd

@@ -0,0 +1,30 @@
+## RoomNavigator — autoload that moves the Camera2D smoothly between hospital floors.
+extends Node
+
+signal room_changed(floor_index: int)
+
+const FLOOR_HEIGHT: float = 720.0
+const CAMERA_TWEEN_DURATION: float = 0.6
+
+var _current_floor: int = 0
+var _camera: Camera2D
+
+
+func initialize(camera: Camera2D) -> void:
+	_camera = camera
+
+
+func go_to_floor(floor_index: int) -> void:
+	if _camera == null or floor_index == _current_floor:
+		return
+	_current_floor = floor_index
+	var target_y: float = floor_index * -FLOOR_HEIGHT
+	var tween: Tween = _camera.create_tween()
+	tween.set_ease(Tween.EASE_IN_OUT)
+	tween.set_trans(Tween.TRANS_SINE)
+	tween.tween_property(_camera, "position:y", target_y, CAMERA_TWEEN_DURATION)
+	room_changed.emit(floor_index)
+
+
+func get_current_floor() -> int:
+	return _current_floor