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)

src/client/components/FabMenu.tsx

@@ -1,5 +1,6 @@
 import { AnimatePresence, motion } from "framer-motion";
 import { Package, Plus, Search } from "lucide-react";
+import { useTranslation } from "react-i18next";
 import { useUIStore } from "../stores/uiStore";
 
 interface FabMenuProps {
@@ -15,6 +16,7 @@ interface MenuItem {
 }
 
 export function FabMenu({ isSetupsPage }: FabMenuProps) {
+	const { t } = useTranslation();
 	const fabMenuOpen = useUIStore((s) => s.fabMenuOpen);
 	const openFabMenu = useUIStore((s) => s.openFabMenu);
 	const closeFabMenu = useUIStore((s) => s.closeFabMenu);
@@ -26,12 +28,12 @@ export function FabMenu({ isSetupsPage }: FabMenuProps) {
 
 	const menuItems: MenuItem[] = [
 		{
-			label: "Add to Collection",
+			label: t("fab.addToCollection"),
 			icon: <Package className="w-5 h-5 text-gray-600" />,
 			onClick: () => openCatalogSearch("collection"),
 		},
 		{
-			label: "Start New Thread",
+			label: t("fab.startNewThread"),
 			icon: <Search className="w-5 h-5 text-gray-600" />,
 			onClick: () => openCatalogSearch("thread"),
 		},
@@ -39,7 +41,7 @@ export function FabMenu({ isSetupsPage }: FabMenuProps) {
 
 	if (isSetupsPage) {
 		menuItems.push({
-			label: "New Setup",
+			label: t("fab.newSetup"),
 			icon: <Plus className="w-5 h-5 text-gray-600" />,
 			onClick: () => {
 				closeFabMenu();