feat: redesign weight summary legend and add currency selector

Redesign WeightSummaryCard stats from a disconnected 4-column grid to a
compact legend-style list with color dots, percentages, and a divider
before the total row. Switch chart and legend colors to a neutral gray
palette.

Add a currency selector to settings (USD, EUR, GBP, JPY, CAD, AUD) that
changes the displayed symbol across the app. This is visual only — no
value conversion is performed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/client/routes/index.tsx

@@ -4,6 +4,7 @@ import { useSetups } from "../hooks/useSetups";
 import { useThreads } from "../hooks/useThreads";
 import { useTotals } from "../hooks/useTotals";
 import { useWeightUnit } from "../hooks/useWeightUnit";
+import { useCurrency } from "../hooks/useCurrency";
 import { formatPrice, formatWeight } from "../lib/formatters";
 
 export const Route = createFileRoute("/")({
@@ -15,6 +16,7 @@ function DashboardPage() {
 	const { data: threads } = useThreads(false);
 	const { data: setups } = useSetups();
 	const unit = useWeightUnit();
+	const currency = useCurrency();
 
 	const global = totals?.global;
 	const activeThreadCount = threads?.length ?? 0;
@@ -33,7 +35,7 @@ function DashboardPage() {
 							label: "Weight",
 							value: formatWeight(global?.totalWeight ?? null, unit),
 						},
-						{ label: "Cost", value: formatPrice(global?.totalCost ?? null) },
+						{ label: "Cost", value: formatPrice(global?.totalCost ?? null, currency) },
 					]}
 					emptyText="Get started"
 				/>