test(core): add the lazy settings modal stories

Written on another branch during the campaign; folding it in so the core batch
carries the complete set.

frontend/editor/src/core/components/shared/AppConfigModalLazy.stories.tsx

@@ -0,0 +1,29 @@
+/**
+ * Lazy wrapper around the settings modal: it renders nothing until opened, so
+ * the heavy config bundle is only fetched when someone asks for settings.
+ *
+ * Sections come from the build's registry, and hosts can add their own or hide
+ * ones they cannot run.
+ */
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import AppConfigModalLazy from "@app/components/shared/AppConfigModalLazy";
+
+const meta: Meta<typeof AppConfigModalLazy> = {
+  title: "Shared/AppConfigModalLazy",
+  component: AppConfigModalLazy,
+  parameters: { layout: "fullscreen" },
+  args: { opened: false, onClose: () => {}, urlSync: false },
+};
+export default meta;
+
+type Story = StoryObj<typeof AppConfigModalLazy>;
+
+/** Closed, which is the state it spends nearly all its life in. */
+export const Closed: Story = {};
+
+export const Opened: Story = { args: { opened: true } };
+
+/** A host that cannot run a registry section drops it by key. */
+export const WithHiddenSection: Story = {
+  args: { opened: true, hiddenSectionKeys: ["about"] as never },
+};