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/components/SetupCard.tsx

@@ -1,4 +1,5 @@
 import { Link } from "@tanstack/react-router";
+import { useWeightUnit } from "../hooks/useWeightUnit";
 import { formatPrice, formatWeight } from "../lib/formatters";
 
 interface SetupCardProps {
@@ -16,6 +17,7 @@ export function SetupCard({
 	totalWeight,
 	totalCost,
 }: SetupCardProps) {
+	const unit = useWeightUnit();
 	return (
 		<Link
 			to="/setups/$setupId"
@@ -30,7 +32,7 @@ export function SetupCard({
 			</div>
 			<div className="flex flex-wrap gap-1.5">
 				<span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-blue-50 text-blue-400">
-					{formatWeight(totalWeight)}
+					{formatWeight(totalWeight, unit)}
 				</span>
 				<span className="inline-flex items-center px-2 py-0.5 rounded-full text-xs font-medium bg-green-50 text-green-500">
 					{formatPrice(totalCost)}