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/CategoryHeader.tsx

@@ -1,5 +1,6 @@
 import { useState } from "react";
 import { useDeleteCategory, useUpdateCategory } from "../hooks/useCategories";
+import { useWeightUnit } from "../hooks/useWeightUnit";
 import { formatPrice, formatWeight } from "../lib/formatters";
 import { LucideIcon } from "../lib/iconData";
 import { IconPicker } from "./IconPicker";
@@ -21,6 +22,7 @@ export function CategoryHeader({
 	totalCost,
 	itemCount,
 }: CategoryHeaderProps) {
+	const unit = useWeightUnit();
 	const [isEditing, setIsEditing] = useState(false);
 	const [editName, setEditName] = useState(name);
 	const [editIcon, setEditIcon] = useState(icon);
@@ -85,7 +87,7 @@ export function CategoryHeader({
 			<h2 className="text-lg font-semibold text-gray-900">{name}</h2>
 			<span className="text-sm text-gray-400">
 				{itemCount} {itemCount === 1 ? "item" : "items"} ·{" "}
-				{formatWeight(totalWeight)} · {formatPrice(totalCost)}
+				{formatWeight(totalWeight, unit)} · {formatPrice(totalCost)}
 			</span>
 			{!isUncategorized && (
 				<div className="ml-auto flex items-center gap-1 opacity-0 group-hover:opacity-100 transition-opacity">