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/main/main.gd

@@ -0,0 +1,16 @@
+## Main — scene root: wires up RoomNavigator and restores saved character positions.
+extends Node2D
+
+
+func _ready() -> void:
+	RoomNavigator.initialize($Camera2D)
+	SaveManager.load_game()
+	_apply_saved_state()
+
+
+func _apply_saved_state() -> void:
+	for character in $Characters.get_children():
+		if character is Character and character.data != null:
+			var pos: Vector2 = GameState.get_character_position(character.data.id)
+			if pos != Vector2.ZERO:
+				character.global_position = pos