chore: update gitignore and restore backend files

- Add backend/node_modules to .gitignore
- Untrack backend/node_modules from git
- Restore backend source files (go.mod, main.go, etc.) that were missing in HEAD
- Include frontend test updates

frontend/src/pages/__tests__/Setup.test.tsx

@@ -1,10 +1,20 @@
-import { render, screen, waitFor } from '@testing-library/react';
+import { render, screen, waitFor, fireEvent } from '@testing-library/react';
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
 import { MemoryRouter } from 'react-router-dom';
 import { vi, describe, it, expect, beforeEach } from 'vitest';
 import Setup from '../Setup';
 import * as setupApi from '../../api/setup';
 
+// Mock react-router-dom
+const mockNavigate = vi.fn();
+vi.mock('react-router-dom', async () => {
+  const actual = await vi.importActual('react-router-dom');
+  return {
+    ...actual,
+    useNavigate: () => mockNavigate,
+  };
+});
+
 // Mock the API module
 vi.mock('../../api/setup', () => ({
   getSetupStatus: vi.fn(),
@@ -57,5 +67,61 @@ describe('Setup Page', () => {
     await waitFor(() => {
       expect(screen.queryByText('Welcome to CPM+')).toBeNull();
     });
+
+    await waitFor(() => {
+      expect(mockNavigate).toHaveBeenCalledWith('/login');
+    });
+  });
+
+  it('submits form successfully', async () => {
+    vi.mocked(setupApi.getSetupStatus).mockResolvedValue({ setupRequired: true });
+    vi.mocked(setupApi.performSetup).mockResolvedValue();
+
+    renderWithProviders(<Setup />);
+
+    await waitFor(() => {
+      expect(screen.getByText('Welcome to CPM+')).toBeTruthy();
+    });
+
+    fireEvent.change(screen.getByLabelText('Name'), { target: { value: 'Admin' } });
+    fireEvent.change(screen.getByLabelText('Email Address'), { target: { value: 'admin@example.com' } });
+    fireEvent.change(screen.getByLabelText('Password'), { target: { value: 'password123' } });
+
+    fireEvent.click(screen.getByRole('button', { name: 'Create Admin Account' }));
+
+    await waitFor(() => {
+      expect(setupApi.performSetup).toHaveBeenCalledWith({
+        name: 'Admin',
+        email: 'admin@example.com',
+        password: 'password123',
+      }, expect.anything());
+    });
+
+    await waitFor(() => {
+      expect(mockNavigate).toHaveBeenCalledWith('/login');
+    });
+  });
+
+  it('displays error on submission failure', async () => {
+    vi.mocked(setupApi.getSetupStatus).mockResolvedValue({ setupRequired: true });
+    vi.mocked(setupApi.performSetup).mockRejectedValue({
+      response: { data: { error: 'Setup failed' } }
+    });
+
+    renderWithProviders(<Setup />);
+
+    await waitFor(() => {
+      expect(screen.getByText('Welcome to CPM+')).toBeTruthy();
+    });
+
+    fireEvent.change(screen.getByLabelText('Name'), { target: { value: 'Admin' } });
+    fireEvent.change(screen.getByLabelText('Email Address'), { target: { value: 'admin@example.com' } });
+    fireEvent.change(screen.getByLabelText('Password'), { target: { value: 'password123' } });
+
+    fireEvent.click(screen.getByRole('button', { name: 'Create Admin Account' }));
+
+    await waitFor(() => {
+      expect(screen.getByText('Setup failed')).toBeTruthy();
+    });
   });
 });