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/characters/character_data.gd

@@ -0,0 +1,12 @@
+## CharacterData — Resource holding all persistent state for one character.
+class_name CharacterData extends Resource
+
+enum State { HEALTHY, SICK, SLEEPING, TIRED, PREGNANT, BABY }
+enum Species { BUNNY, KITTEN }
+
+@export var id: String = ""
+@export var display_name: String = ""
+@export var species: Species = Species.BUNNY
+@export var state: State = State.HEALTHY
+@export var current_floor: int = 0
+@export var position: Vector2 = Vector2.ZERO