Fix crashes on unknown menu item / order routes

Both loaders threw a plain Error that the router doesn't treat as a
route-level not-found, so visiting /items/<bad-id> or /orders/<bad-id>
(or a valid order with a missing/wrong ?token) crashed instead of
showing the NotFound page. Menu item lookups now throw notFound()
directly; the order loader catches the server function's error and
maps both "order not found" and "wrong access token" to notFound(),
so a guessed id can't be used to probe which orders exist.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/routes/items/$menuItemId.tsx

@@ -1,4 +1,4 @@
-import { Link, createFileRoute } from '@tanstack/react-router'
+import { Link, createFileRoute, notFound } from '@tanstack/react-router'
 
 import { MenuItemDetail } from '#/components/ordering/MenuItemDetail.tsx'
 import { useBasket } from '#/lib/basket.tsx'
@@ -48,7 +48,7 @@ export const Route = createFileRoute('/items/$menuItemId')({
     const brand = await getBrand()
     const menu = await getMenu({ data: { brandId: brand.id } })
     const item = menu.find((menuItem) => menuItem.id === Number(params.menuItemId))
-    if (!item) throw new Error('Menu item not found')
+    if (!item) throw notFound()
     return { item }
   },
   component: MenuItemRoute,

src/routes/orders/$orderId.tsx

@@ -1,4 +1,4 @@
-import { createFileRoute } from '@tanstack/react-router'
+import { createFileRoute, notFound } from '@tanstack/react-router'
 import { z } from 'zod'
 
 import { OrderStatusView } from '#/components/orders/OrderStatusView.tsx'
@@ -6,6 +6,16 @@ import { getOrderStatus } from '#/server/orders.ts'
 
 const searchSchema = z.object({ token: z.string().optional() })
 
+// Errors cross the server-function boundary as a plain `Error` carrying only
+// `.message` (TanStack Start's ShallowErrorPlugin drops the subclass), so an
+// unknown order and a wrong/missing guest token are told apart by message
+// rather than `instanceof`. Both collapse to a 404 rather than a real error
+// page, so a guessed order id can't be used to probe which ones exist.
+const notFoundMessages = new Set([
+  'Order not found',
+  'You do not have access to this Order',
+])
+
 const OrderStatusRoute = () => {
   const status = Route.useLoaderData()
   const { token } = Route.useSearch()
@@ -17,12 +27,20 @@ export const Route = createFileRoute('/orders/$orderId')({
   validateSearch: (search: Record<string, unknown>) =>
     searchSchema.parse(search),
   loaderDeps: ({ search }) => ({ token: search.token }),
-  loader: ({ params, deps }) =>
+  loader: async ({ params, deps }) => {
-    getOrderStatus({
+    try {
+      return await getOrderStatus({
         data: {
           orderId: Number(params.orderId),
           guestAccessToken: deps.token,
         },
-    }),
+      })
+    } catch (error) {
+      if (error instanceof Error && notFoundMessages.has(error.message)) {
+        throw notFound()
+      }
+      throw error
+    }
+  },
   component: OrderStatusRoute,
 })