Add Playwright E2E Tests to Next.js (Cursor Prompt)

Add Playwright end-to-end tests to this Next.js application.

FILES TO CREATE:
- playwright.config.ts — Playwright configuration
- tests/auth.spec.ts — Authentication flow tests
- tests/crud.spec.ts — CRUD operation tests
- tests/payments.spec.ts — Payment flow tests
- tests/fixtures.ts — Shared test fixtures and helpers
- tests/helpers/auth.ts — Auth helper functions

CONFIGURATION:
- Use Chromium only for CI speed. Use all browsers locally.
- Base URL: http://localhost:3000
- Add webServer config to auto-start Next.js dev server.
- Enable trace on first retry for debugging.
- Screenshots on failure.

TEST SUITES:
1. Auth tests: signup, signin, password reset, protected route redirect, signout
2. CRUD tests: create item, read list, update item, delete item, form validation errors
3. Payment tests: view pricing, start checkout (mock Stripe in test mode), handle success redirect

PATTERNS:
- Use Page Object Model: create page objects for each page (LoginPage, DashboardPage, etc.).
- Create a test user fixture that signs up before tests and cleans up after.
- Use data-testid attributes for selecting elements (never rely on CSS classes or text content).
- Run tests in isolation — each test should not depend on another test's state.

DO NOT:
- Modify application code (except adding data-testid attributes)
- Test third-party services (mock Stripe)
- Write flaky tests that depend on timing (use waitFor and expect patterns)