The input mapper called Brazilian Portuguese `pt` while the repository's own
docs use `pt-BR` (docs/user/README.pt-BR.md, "Português (Brasil)"). Rename the
locale code and its message table to `pt-BR`, label it "Português (Brasil)",
and keep a saved `pt` choice working by mapping it to `pt-BR` in
initialLocale.
AI-assisted: yes
Translate the 32 message keys the Portuguese catalogue lacked: the skip link,
the navigation and section labels, the replace and capture dialogs, the import,
clipboard and download statuses, and the per-binding accessibility labels.
Use "atribuição" for a binding and keep "entrada" for a keyboard or mouse
input in the strings that already said "entrada".
mrph28