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>

scenes/objects/ElevatorButton.tscn

@@ -0,0 +1,29 @@
+[gd_scene load_steps=3 format=3 uid="uid://cozypaw_elevator_btn"]
+
+[ext_resource type="Script" path="res://scripts/objects/elevator_button.gd" id="1_elevbtn"]
+
+[sub_resource type="RectangleShape2D" id="RectangleShape2D_elevbtn"]
+size = Vector2(80, 80)
+
+[node name="ElevatorButton" type="Node2D"]
+script = ExtResource("1_elevbtn")
+
+[node name="Visual" type="ColorRect" parent="."]
+color = Color(0.95, 0.75, 0.3, 1)
+size = Vector2(80, 80)
+position = Vector2(-40, -40)
+
+[node name="Label" type="Label" parent="Visual"]
+offset_left = 0.0
+offset_top = 0.0
+offset_right = 80.0
+offset_bottom = 80.0
+horizontal_alignment = 1
+vertical_alignment = 1
+text = "▲"
+
+[node name="CollisionArea" type="Area2D" parent="."]
+input_pickable = true
+
+[node name="CollisionShape" type="CollisionShape2D" parent="CollisionArea"]
+shape = SubResource("RectangleShape2D_elevbtn")