Dashboard available in French and German

The dashboard UI is now available in three languages: English (default), French, and German. Each user picks their language from the Language submenu in the user menu; the choice is saved and persists across sessions. On first visit the language follows the browser's preference, falling back to English. Dates and numbers are formatted for the active language.

This localizes the dashboard UI only. The AI Shopping Assistant's replies are unaffected. It is multilingual and answers in the shopper's own language regardless of the dashboard setting.