Add main menu, WebSocket API demo, and multi-scene game hub.

Replace the single-entry Pong flow with a menu launcher, a per-client API demo on :8081/ws with stream controls and tap flash feedback, and bump the viewport to 1920×1080.

Co-authored-by: Cursor <cursoragent@cursor.com>

scripts/menu.gd

@@ -0,0 +1,28 @@
+extends Control
+
+const DEMO_SCENE := "res://scenes/demo.tscn"
+const CONFIG_SCENE := "res://scenes/config.tscn"
+const PONG_SCENE := "res://scenes/pong.tscn"
+const COLOR_GAME_SCENE := "res://scenes/color_game.tscn"
+
+@onready var demo_button: Button = $CenterBox/DemoButton
+@onready var config_button: Button = $CenterBox/ConfigButton
+@onready var pong_button: Button = $CenterBox/PongButton
+@onready var color_game_button: Button = $CenterBox/ColorGameButton
+@onready var exit_button: Button = $CenterBox/ExitButton
+
+
+func _ready() -> void:
+	demo_button.pressed.connect(func(): _open_scene(DEMO_SCENE))
+	config_button.pressed.connect(func(): _open_scene(CONFIG_SCENE))
+	pong_button.pressed.connect(func(): _open_scene(PONG_SCENE))
+	color_game_button.pressed.connect(func(): _open_scene(COLOR_GAME_SCENE))
+	exit_button.pressed.connect(_exit_game)
+
+
+func _open_scene(path: String) -> void:
+	get_tree().change_scene_to_file(path)
+
+
+func _exit_game() -> void:
+	get_tree().quit()