[e2e-examiner-ui] Examiner UI: run end-to-end tests as part of the GitHub CD pipeline

## Summary

The Examiner UI’s CD pipeline on GitHub should run and report on automated end-to-end tests so regressions are caught post deployment on target environments.

## Acceptance criteria

- The Examiner UI CD pipeline runs the Examiner e2e suite immediately after deployment so that the tests run against the new version of the application.
- Required secrets and environment configuration for a headless run are available to the workflow without exposing them in logs or artifacts.
- Test results (reports, traces, or videos, per team policy) are retained as build artifacts.