feat(07-02): add weight unit toggle and wire all formatWeight call sites

- Add segmented g/oz/lb/kg toggle to TotalsBar with settings persistence
- Pass unit parameter to all 8 formatWeight call sites across components and routes
- Import useWeightUnit hook in ItemCard, CandidateCard, CategoryHeader, SetupCard, ItemPicker, Dashboard, SetupDetail

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

src/client/routes/index.tsx

@@ -3,6 +3,7 @@ import { DashboardCard } from "../components/DashboardCard";
 import { useSetups } from "../hooks/useSetups";
 import { useThreads } from "../hooks/useThreads";
 import { useTotals } from "../hooks/useTotals";
+import { useWeightUnit } from "../hooks/useWeightUnit";
 import { formatPrice, formatWeight } from "../lib/formatters";
 
 export const Route = createFileRoute("/")({
@@ -13,6 +14,7 @@ function DashboardPage() {
 	const { data: totals } = useTotals();
 	const { data: threads } = useThreads(false);
 	const { data: setups } = useSetups();
+	const unit = useWeightUnit();
 
 	const global = totals?.global;
 	const activeThreadCount = threads?.length ?? 0;
@@ -29,7 +31,7 @@ function DashboardPage() {
 						{ label: "Items", value: String(global?.itemCount ?? 0) },
 						{
 							label: "Weight",
-							value: formatWeight(global?.totalWeight ?? null),
+							value: formatWeight(global?.totalWeight ?? null, unit),
 						},
 						{ label: "Cost", value: formatPrice(global?.totalCost ?? null) },
 					]}