HTML Architect: Add end-to-end (E2E) tests with Playwright

HTML Architect currently has no end-to-end test coverage. Following the discussion with Pavel and Jindra, the recommended approach is to introduce a modern E2E testing setup based on Playwright.

Why Playwright

Playwright is currently the best E2E framework, according to 2026 benchmark data
Sources for reference:

Goal

Set up a Playwright-based E2E testing infrastructure for HTML Architect

Scope / acceptance criteria

  • Playwright installed and configured in the HTML Architect project
  • CI integration tests run on PRs