feat: 引入 yuxiang-kit 课程组件源码与运行时

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

src/course-runtime/canvas/index.ts

@@ -0,0 +1,7 @@
+export { CanvasContext, useCourseCanvas } from "./CanvasContext";
+export { CourseCanvas } from "./CourseCanvas";
+export type {
+	CourseCanvasContextValue,
+	CourseCanvasProps,
+	CourseCanvasViewport,
+} from "./CourseCanvas.types";