Add Python Playwright QA test suite

[gregjkal]

Migrates and extends the Playwright QA test suite from karimarie67/QA-documentation into the main repo.

• Adds qa/ directory with smoke, boost.io, version, documentation, download/search, and error handling tests
• Adds a Playwright Docker service (docker/Dockerfile.playwright) and just qa target for running tests against staging or production
• Adds pytest-playwright to requirements
• Tests are black-box browser tests run via pytest --env=staging (or --env=production)