Fix headless Toast e2e selector ambiguity

[Copilot]

The CI / e2e (pull_request) job failed because [data-intent] matched both each toast root and its ToastTitle media slot, doubling Cypress element counts.

• Test selectors: Use the unique ToastContainer structural role for toast assertions and hover interactions.

const TOAST_CONTAINER = '[role="listitem"]';

cy.get(TOAST_CONTAINER).should('have.length', 5);