fix(scripts): exempt Storybook stories from coverage:diff gate

Story files are excluded from vitest by design (they run in Storybook
runner, not vitest). Add *.stories.{ts,tsx} to ALLOWED_GLOBS so the
L1 diff gate doesn't flag them as "new untested file".

Also add error-handling test for useOptionalConsent rethrow path
(cookie-consent-banner lines 52-53) achieving 100% statement coverage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-ui/src/cookie-consent-banner/cookie-consent-banner-unexpected-error.test.tsx

@@ -0,0 +1,61 @@
+/**
+ * Isolated test file for the error-re-throw path in useOptionalConsent.
+ * Uses vi.mock to make useConsent throw a non-ConsentContextError so that
+ * lines 52-53 (the `throw e` branch) are exercised.
+ */
+import { describe, it, expect, vi } from "vitest";
+import { Component, type ReactNode } from "react";
+import { render, screen } from "@testing-library/react";
+
+vi.mock("@repo/core-consent/react", () => ({
+  useConsent: vi.fn(() => {
+    throw new Error("unexpected-non-consent-error");
+  }),
+  ConsentContextError: class ConsentContextError extends Error {
+    constructor() {
+      super("no provider");
+      this.name = "ConsentContextError";
+    }
+  },
+}));
+
+import { CookieConsentBanner } from "./cookie-consent-banner";
+
+class ErrorBoundary extends Component<
+  { children: ReactNode },
+  { caught: string | null }
+> {
+  constructor(props: { children: ReactNode }) {
+    super(props);
+    this.state = { caught: null };
+  }
+
+  static getDerivedStateFromError(error: Error) {
+    return { caught: error.message };
+  }
+
+  render() {
+    if (this.state.caught) {
+      return <div data-testid="caught">{this.state.caught}</div>;
+    }
+    return this.props.children;
+  }
+}
+
+describe("CookieConsentBanner — useOptionalConsent rethrows non-ConsentContextError", () => {
+  it("surfaces unexpected render errors through an error boundary", () => {
+    const consoleSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    render(
+      <ErrorBoundary>
+        <CookieConsentBanner variant="modal" />
+      </ErrorBoundary>,
+    );
+
+    expect(screen.getByTestId("caught")).toHaveTextContent(
+      "unexpected-non-consent-error",
+    );
+
+    consoleSpy.mockRestore();
+  });
+});