tests: e2e testing course

[olekszczepanowski]

bez logowania

• tworzenie, edycja, usuwanie i udostępnianie planów
• pobieranie planów w różnych formatach
• feedback form

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[!IMPORTANT] Add end-to-end tests for course planning features using Playwright, including plan creation, editing, deletion, sharing, and feedback form validation.

• Testing:
  • Adds end-to-end tests in tests/tests.spec.ts for creating, editing, deleting, and sharing plans.
  • Tests downloading plans as .png and .ics files.
  • Tests feedback form validation for email, title, and description.
• Configuration:
  • Adds Playwright configuration in playwright.config.ts.
  • Updates .gitignore to include Playwright-related files.
  • Adds @playwright/test to devDependencies in package.json.
• Components:
  • Adds data-testid attributes to buttons in page.client.tsx, plan-display-link.tsx, and plan-item.tsx for testability.
  • Updates validation messages in schemas.ts for feedback form.

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