feat(frontend): widget registry + universal fallback

frontend/src/widgets/registry.ts

@@ -0,0 +1,13 @@
+import type React from "react";
+import type { WidgetProps } from "./types";
+import { FallbackWidget } from "./FallbackWidget";
+
+const registry = new Map<string, React.FC<WidgetProps>>();
+
+export function register(kind: string, comp: React.FC<WidgetProps>) {
+  registry.set(kind, comp);
+}
+
+export function resolve(kind: string): React.FC<WidgetProps> {
+  return registry.get(kind) ?? FallbackWidget;
+}