refactor: CourseCanvas 使用默认画布尺寸，移除冗余 width/height 配置

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/App.tsx

@@ -1,6 +1,5 @@
 import { useEffect } from "react";
 import { Outlet } from "react-router-dom";
-import { appConfig } from "@/app.config";
 import { ToastProvider, ToastViewport } from "@/components/ui/toast";
 import { CourseCanvas, useCourseCanvas } from "@/course-runtime/canvas";
 import { OrientationGuard } from "@/course-runtime/orientation";
@@ -65,8 +64,6 @@ function App() {
 		<>
 			<OrientationGuard />
 			<CourseCanvas
-				width={appConfig.design.width}
-				height={appConfig.design.height}
 				className="bg-gray-900"
 				canvasClassName="flex flex-col overflow-hidden bg-white"
 			>