Add unit tests for OAuthButtons and LinkedAccountsSettings components

- Introduced comprehensive test coverage for `OAuthButtons` and `LinkedAccountsSettings`, including loading states, button behaviors, error handling, and custom class support.
- Implemented `LinkedAccountsPage` tests for rendering and component integration.
- Adjusted E2E coverage exclusions in various components, focusing on UI-heavy and animation-based flows best suited for E2E tests.
- Refined Jest coverage thresholds to align with improved unit test additions.

frontend/tests/app/settings/accounts/page.test.tsx

@@ -0,0 +1,41 @@
+/**
+ * Tests for Linked Accounts Settings Page
+ */
+
+import { render, screen } from '@testing-library/react';
+import LinkedAccountsPage from '@/app/[locale]/(authenticated)/settings/accounts/page';
+
+// Mock next-intl
+jest.mock('next-intl', () => ({
+  useTranslations: () => (key: string) => {
+    const translations: Record<string, string> = {
+      pageTitle: 'Linked Accounts',
+      pageSubtitle: 'Manage your linked social accounts for quick sign-in',
+    };
+    return translations[key] || key;
+  },
+}));
+
+// Mock the LinkedAccountsSettings component
+jest.mock('@/components/settings', () => ({
+  LinkedAccountsSettings: () => (
+    <div data-testid="linked-accounts-settings">Mocked LinkedAccountsSettings</div>
+  ),
+}));
+
+describe('LinkedAccountsPage', () => {
+  it('renders page title and subtitle', () => {
+    render(<LinkedAccountsPage />);
+
+    expect(screen.getByText('Linked Accounts')).toBeInTheDocument();
+    expect(
+      screen.getByText('Manage your linked social accounts for quick sign-in')
+    ).toBeInTheDocument();
+  });
+
+  it('renders LinkedAccountsSettings component', () => {
+    render(<LinkedAccountsPage />);
+
+    expect(screen.getByTestId('linked-accounts-settings')).toBeInTheDocument();
+  });
+});