feat: add Playwright E2E testing framework

Add @playwright/test, playwright.config.ts, e2e/ smoke test,
and e2e CI job (Chromium-only) that gates build-and-push.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

e2e/smoke.spec.ts

@@ -0,0 +1,6 @@
+import { test, expect } from '@playwright/test';
+
+test('app loads', async ({ page }) => {
+  await page.goto('/');
+  await expect(page).toHaveTitle(/CartSnitch/);
+});

package.json

@@ -9,7 +9,8 @@
     "lint": "eslint .",
     "preview": "vite preview",
     "test": "NODE_ENV=test vitest run",
-    "test:watch": "NODE_ENV=test vitest"
+    "test:watch": "NODE_ENV=test vitest",
+    "test:e2e": "npx playwright test"
   },
   "dependencies": {
     "@tanstack/react-query": "^5.0.0",
@@ -32,6 +33,7 @@
     "eslint": "^9.39.4",
     "eslint-plugin-react-hooks": "^7.0.1",
     "eslint-plugin-react-refresh": "^0.5.2",
+    "@playwright/test": "^1.49.0",
     "globals": "^17.4.0",
     "jsdom": "^25.0.1",
     "tailwindcss": "^4.0.0",

playwright.config.ts

@@ -0,0 +1,19 @@
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './e2e',
+  projects: [
+    {
+      name: 'chromium',
+      use: { ...devices['Desktop Chrome'] },
+    },
+  ],
+  webServer: {
+    command: 'npm run dev',
+    url: 'http://localhost:5173',
+    reuseExistingServer: !process.env.CI,
+  },
+  use: {
+    baseURL: 'http://localhost:5173',
+  },
+});