Add persistent light and dark themes

scripts/ui/main.gd

@@ -9,11 +9,15 @@ var user_label: Label
 var app_menu: PanelContainer
 var menu_exit_button: Button
 var sound_toggle: CheckButton
+var theme_button: Button
+var theme_service
 var current_screen_name := ""
 
 func _ready() -> void:
+	theme_service = get_node("/root/UIThemeService")
 	Style.apply_app_theme(self)
 	_build_ui()
+	theme_service.theme_changed.connect(_on_theme_changed)
 	resized.connect(_update_responsive_layout)
 	_update_responsive_layout()
 	show_screen("selection" if AuthState.is_logged_in else "login", "exam")
@@ -92,6 +96,14 @@ func _build_ui() -> void:
 	user_label.gui_input.connect(_on_user_label_gui_input)
 	header.add_child(user_label)
 
+	theme_button = Button.new()
+	theme_button.custom_minimum_size = Vector2(44, 44)
+	theme_button.add_theme_font_size_override("font_size", 22)
+	UISoundService.set_button_sound(theme_button, "toggle")
+	theme_button.pressed.connect(theme_service.toggle_theme)
+	header.add_child(theme_button)
+	_refresh_theme_button()
+
 	var screens_container := MarginContainer.new()
 	screens_container.name = "Screens"
 	screens_container.size_flags_vertical = Control.SIZE_EXPAND_FILL
@@ -176,6 +188,22 @@ func _refresh_header_stats() -> void:
 		user_label.text = AuthState.username if AuthState.is_logged_in else ""
 
 
+func _on_theme_changed(is_dark_mode: bool) -> void:
+	Style.refresh_tree(self, not is_dark_mode)
+	_refresh_theme_button()
+	var player = screens.get("player")
+	if player != null and player.has_method("refresh_theme_controls"):
+		player.refresh_theme_controls()
+
+
+func _refresh_theme_button() -> void:
+	if theme_button == null:
+		return
+	theme_button.text = "☀" if theme_service.is_dark_mode() else "☾"
+	theme_button.tooltip_text = "Switch to light mode" if theme_service.is_dark_mode() else "Switch to dark mode"
+	Style.style_chip(theme_button, Style.CYAN)
+
+
 func _logout() -> void:
 	_close_app_menu()
 	if BlockSessionService.block_started: