feat(orders): show the receipt in the transaction detail panel

`expense_metadata` has held the itemised receipt since ingestion started and
nothing in the UI ever read it. A transaction that came from a DoorDash or Uber
Eats receipt showed a merchant and an amount, with the item list and the
delivery addresses sitting unread in the row behind it (user, 2026-07-27).

Adds GET /api/transactions/[id]/order and an "Order details" section in the
edit modal: line items with their options, pick-up/delivery stops with times
and addresses, the card tail when one was involved, and the provider's own
order reference.

Two details that matter:

- The lookup resolves from **both** sides — `transaction_id` OR
  `matched_transaction_id`. A card-settled order creates no transaction of its
  own (I5); the receipt points at the statement line instead. Matching only on
  transaction_id would have left the panel blank on exactly the card-paid
  orders, which are the ones whose detail is hardest to find elsewhere.
- An empty item list says so in words rather than rendering nothing. Uber
  itemises groceries but not restaurant orders, and orders ingested before the
  Uber item parser existed have none either — a blank section reads as a bug
  when it is usually the receipt.

Read-only. This is what a provider sent; editing it would make provenance mean
nothing.

src/lib/hooks.ts

@@ -250,6 +250,33 @@ export function useTransactionSplits(transactionId: number) {
   });
 }
 
+export interface OrderReceipt {
+  platform: "doordash" | "ubereats" | "uber" | null;
+  order_reference: string | null;
+  line_items: { qty: number; description: string; amount: number; options?: string[] }[];
+  route: { label: string; time: string | null; address: string }[];
+  subtotal: string | null;
+  amount: string | null;
+  currency: string | null;
+  card_last4: string | null;
+  flags: string[];
+  source_email_subject: string | null;
+  transaction_date: string | null;
+}
+
+/** The receipt behind a transaction, or null when it did not come from one. */
+export function useOrderReceipt(transactionId: number) {
+  return useQuery<OrderReceipt | null>({
+    queryKey: ["order-receipt", transactionId],
+    queryFn: async () => {
+      const res = await fetch(`/api/transactions/${transactionId}/order`);
+      if (!res.ok) return null;
+      return res.json();
+    },
+    staleTime: Infinity, // a receipt never changes
+  });
+}
+
 export function useSetSplits() {
   const qc = useQueryClient();
   return useMutation({