Only the mail shell updated document.title, so every other surface sat at the
static value the root layout renders: the tab could not tell you where you
were, and on a multi-account setup it could not tell you whose mailbox you
were in either.
Each surface now sets "<screen> - <account> - <app>" through the shared
useDocumentTitle hook. Labels reuse the sidebar navigation translations, so
the tab and the rail never disagree about what a screen is called - no new
translation keys.
Refs #1159
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>