Update README files for developer onboarding and remove outdated docs

- Rewrite main README.md to focus on Playwright introduction for new developers
- Emphasize prerequisite of running all services (Angular, API, STS) before tests
- Add comprehensive debugging section with UI mode, debug mode, and trace viewer
- Update test user credentials to match actual IdentityServer configuration
- Add PLAYWRIGHT_GUIDE.md and PAGE_OBJECT_BENEFITS.md to docs/README.md
- Include Quick Navigation, Additional Resources, and Recommended Reading Order
- Remove outdated session summaries and fix checklists from docs folder

Author: workcontrolgit