feat: 模板适配层、易班能力与全局状态

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

src/components/common/canvasPortal.ts

@@ -0,0 +1,16 @@
+import type { RefObject } from "react";
+
+let portalRoot: RefObject<HTMLDivElement | null> | null = null;
+
+export function registerAppPortalRoot(
+	container: RefObject<HTMLDivElement | null>,
+): () => void {
+	portalRoot = container;
+	return () => {
+		if (portalRoot === container) portalRoot = null;
+	};
+}
+
+export function getAppPortalRoot(): HTMLDivElement | null {
+	return portalRoot?.current ?? null;
+}