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/lib/api/admin.test.ts

@@ -0,0 +1,67 @@
+/**
+ * Tests for lib/api/admin.ts
+ */
+
+import { getAdminStats } from '@/lib/api/admin';
+import { apiClient } from '@/lib/api/client';
+
+// Mock the apiClient
+jest.mock('@/lib/api/client', () => ({
+  apiClient: {
+    get: jest.fn(),
+  },
+}));
+
+describe('getAdminStats', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+  });
+
+  it('calls apiClient.get with correct parameters', async () => {
+    const mockResponse = {
+      user_growth: [],
+      organization_distribution: [],
+      registration_activity: [],
+      user_status: [],
+    };
+
+    (apiClient.get as jest.Mock).mockResolvedValue(mockResponse);
+
+    await getAdminStats();
+
+    expect(apiClient.get).toHaveBeenCalledWith({
+      responseType: 'json',
+      security: [
+        {
+          scheme: 'bearer',
+          type: 'http',
+        },
+      ],
+      url: '/api/v1/admin/stats',
+    });
+  });
+
+  it('uses custom client when provided', async () => {
+    const customClient = {
+      get: jest.fn().mockResolvedValue({}),
+    };
+
+    await getAdminStats({ client: customClient as any });
+
+    expect(customClient.get).toHaveBeenCalled();
+    expect(apiClient.get).not.toHaveBeenCalled();
+  });
+
+  it('passes through additional options', async () => {
+    (apiClient.get as jest.Mock).mockResolvedValue({});
+
+    await getAdminStats({ throwOnError: true } as any);
+
+    expect(apiClient.get).toHaveBeenCalledWith(
+      expect.objectContaining({
+        url: '/api/v1/admin/stats',
+        throwOnError: true,
+      })
+    );
+  });
+});