feat(i18n): extract strings from navigation, dialogs, onboarding, settings, and login
- Add useTranslation() to TopNav, BottomTabBar, FabMenu, UserMenu
- Internationalize ConfirmDialog, AuthPromptModal, ExternalLinkDialog
- Extract all onboarding flow strings (Welcome, HobbyPicker, ItemBrowser, Review, Done)
- Internationalize settings page (weight unit, currency, API keys, import/export)
- Internationalize login page and root error boundary
- All dialogs in __root.tsx use t() for UI chrome
Phase 34, Plan 02 (core navigation and global UI)