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/hud.gd

@@ -1,10 +1,11 @@
-## HUD — heads-up display with back button and music toggle.
+## HUD — heads-up display with back button, music toggle, and settings access.
 extends CanvasLayer
 
 const MUSIC_ON_SYMBOL: String = "♪"
 const MUSIC_OFF_SYMBOL: String = "✕"
 
 var _music_enabled: bool = true
+@onready var _settings_menu: SettingsMenu = get_node_or_null("/root/Main/UI/SettingsMenu") as SettingsMenu
 
 
 func _on_back_button_pressed() -> void:
@@ -18,3 +19,8 @@ func _on_music_toggle_pressed() -> void:
 	var btn: Button = get_node_or_null("MusicToggle") as Button
 	if btn != null:
 		btn.text = MUSIC_ON_SYMBOL if _music_enabled else MUSIC_OFF_SYMBOL
+
+
+func _on_settings_button_pressed() -> void:
+	if _settings_menu != null:
+		_settings_menu.show_menu()