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/ui/HUD.tscn

@@ -31,5 +31,19 @@ offset_bottom = 80.0
 text = "♪"
 flat = false
 
+[node name="SettingsButton" type="Button" parent="."]
+anchors_preset = 1
+anchor_left = 1.0
+anchor_top = 0.0
+anchor_right = 1.0
+anchor_bottom = 0.0
+offset_left = -160.0
+offset_top = 16.0
+offset_right = -96.0
+offset_bottom = 80.0
+text = "⚙"
+flat = false
+
 [connection signal="pressed" from="BackButton" to="." method="_on_back_button_pressed"]
 [connection signal="pressed" from="MusicToggle" to="." method="_on_music_toggle_pressed"]
+[connection signal="pressed" from="SettingsButton" to="." method="_on_settings_button_pressed"]