feat: wire currency conversion into price display

useFormatters().price() now accepts an optional sourceCurrency param.
When showConversions is enabled and the source differs from the user's
currency, it converts via ECB rates and shows dual format:
"€200.00 (~$218.00)". ItemCard and CollectionView pass priceCurrency
through from API data. Setup detail items also pass priceCurrency.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/components/ItemCard.tsx

@@ -26,6 +26,7 @@ interface ItemCardProps {
 	classification?: string;
 	onClassificationCycle?: () => void;
 	linkTo?: string | null;
+	priceCurrency?: string | null;
 }
 
 export function ItemCard({
@@ -48,6 +49,7 @@ export function ItemCard({
 	classification,
 	onClassificationCycle,
 	linkTo,
+	priceCurrency,
 }: ItemCardProps) {
 	const { weight, price } = useFormatters();
 	const navigate = useNavigate();
@@ -232,7 +234,7 @@ export function ItemCard({
 					)}
 					{priceCents != null && (
 						<span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-green-50 text-green-500">
-							{price(priceCents)}
+							{price(priceCents, priceCurrency)}
 						</span>
 					)}
 					<span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-gray-50 text-gray-600">