* feat: add fullscreen toggle and return-to-page logout redirect
Add a Stimulus-driven fullscreen button/keypress to the quiz and
elimination screens, and redirect admins back to the page they were on
after logging out (unless it was a backoffice or elimination page).
* docs: expand CLAUDE.md domain context and testing conventions
Document the WIDM quiz/elimination domain model in more depth, and add
guidance to prefer plain TestCase over WebTestCase/KernelTestCase and to
apply the Boy Scout Rule for small nearby cleanups.
* fix: drop f-keypress fullscreen shortcut
Candidate names can start with "f" while typing, so the keypress
conflicted with the enter-name form. Button-only toggle remains.
