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/settings_menu.gd

@@ -0,0 +1,37 @@
+## SettingsMenu — overlay panel for audio volume and game reset.
+class_name SettingsMenu extends CanvasLayer
+
+
+func _ready() -> void:
+	visible = false
+
+
+func show_menu() -> void:
+	visible = true
+
+
+func hide_menu() -> void:
+	visible = false
+
+
+func _on_music_slider_value_changed(value: float) -> void:
+	AudioManager.set_music_volume(value)
+
+
+func _on_sfx_slider_value_changed(value: float) -> void:
+	AudioManager.set_sfx_volume(value)
+
+
+func _on_reset_button_pressed() -> void:
+	var dialog: ConfirmationDialog = get_node_or_null("Panel/ResetConfirmDialog") as ConfirmationDialog
+	if dialog != null:
+		dialog.popup_centered()
+
+
+func _on_reset_confirmed() -> void:
+	SaveManager.reset_game()
+	get_tree().reload_current_scene()
+
+
+func _on_close_button_pressed() -> void:
+	hide_menu()