Adds a standalone Playwright (TypeScript) suite under tests/e2e/ui that drives
the Admin UI in a real browser. The single spec logs in as the proxy admin,
creates a virtual key scoped to one model through the create-key modal, then
asserts both halves of the contract: /key/info reflects the alias and model the
form set, and the generated key serves /chat/completions on its scoped model
while being denied key_model_access_denied on a model outside that scope.
The suite is decoupled from the Python harness in the sibling folders; it carries
its own package.json and playwright.config.ts and runs with npm test.
