fix: playwright tests after render-engine migration

[danielcristho]

Issue Link 🔗: #750

Issue: #750

Type of Change

• Bug fix 🐞
• New feature/page
• Documentation update
• Other

Description 📋

• What: Provide an overview of the issue this PR addresses. Explain the context and background information.

• Why: Describe why the changes are being made. Highlight key updates, new features, or bug fixes.

• How: Explain how these changes will affect the project or end-users.

Checklist ✅

• Followed the Code of Conduct and Contribution Guide
• Ran pre-commit run --all
• All tests pass locally
• Added tests (if applicable)
• Documentation updated (if applicable)
• Removed all remaining Jekyll-specific code from the design tests
• Fix playwright test server startup by using pre-built static files
• Update test routes to match render-engine output structure
• Add missing alt text to BPD logo image for accessibility
• Add title and aria-label to donation iframe for screen readers
• Replace xprocess with simple HTTP server for better reliability

Additional Notes & Screenshots

Before: Playwright tests were failing with server startup timeouts and accessibility violations were blocking deployment.

After: All tests pass reliably, accessibility compliance achieved, and deployment works correctly with render-engine.

• uv run python -m pytest tests/test.py::test_accessibility -v -s

• uv run python -m pytest tests/test.py::test_destination -v

• uv run python -m pytest tests/test_design.py -m design --maxfail=1

Add any additional notes or comments that might be helpful for the reviewers.