test(e2e): setup Playwright with login smoke test

- Installed @playwright/test + Chromium
- playwright.config.js: baseURL localhost:5001, Desktop Chrome
- tests/e2e/login.spec.js: validates login form loads and invalid
  credentials show error

tests/e2e/login.spec.js

@@ -0,0 +1,25 @@
+const { test, expect } = require('@playwright/test');
+
+test.describe('Nexus POS — Login', () => {
+  test('login page loads with form', async ({ page }) => {
+    await page.goto('/pos/login');
+    await expect(page).toHaveTitle(/Nexus|Login/i);
+    await expect(page.locator('input[name="username"], input[name="email"], #username, #email')).toBeVisible();
+    await expect(page.locator('input[type="password"], #password')).toBeVisible();
+    await expect(page.locator('button[type="submit"], .btn--primary')).toBeVisible();
+  });
+
+  test('invalid credentials show error', async ({ page }) => {
+    await page.goto('/pos/login');
+    const userInput = page.locator('input[name="username"], input[name="email"], #username, #email').first();
+    const passInput = page.locator('input[type="password"], #password').first();
+    const submitBtn = page.locator('button[type="submit"], .btn--primary').first();
+
+    await userInput.fill('invalid_user');
+    await passInput.fill('wrong_password');
+    await submitBtn.click();
+
+    // Expect error toast or message
+    await expect(page.locator('.toast, .alert, .error, [role="alert"]')).toBeVisible({ timeout: 5000 });
+  });
+});