Add a per-locale common dictionary at src/lib/i18n/common/{de,en}.ts and
the shim src/lib/js/commonI18n.ts. Migrate inline lang ternaries on the
homepage (welcome/sections/links), OfflineSyncButton (all label
ternaries), DatePicker (today/select date), ErrorView (Error/Fehler
eyebrow), and UserHeader (login aria/title) to use the shared dict.
The long marketing intro paragraphs on the homepage stay inline since
they're one-shot content with no drift risk and don't benefit from
per-key extraction.
Bump site version to 1.57.0 (new namespace).
Alexander
79f4dbb101
