Add Playwright E2E tests covering proxy admin team and key management
workflows, with a self-contained test runner and CircleCI integration.
Tests cover: create team, invite user, edit/delete team members, create
key in team, regenerate key, update TPM/RPM limits, delete key, and
verify internal user keys are visible.
Infrastructure: run_e2e.sh builds the UI from source before starting
the proxy, ensuring tests always run against the latest UI changes.
Added data-testid attributes to key UI components for reliable selectors.
d09d98a70a