transactions: never print a foreign amount as AUD

The amount cell rendered formatAmount(amount_aud ?? amount) with no currency
argument, so a row with no AUD figure fell back to its native amount and was
stamped with a dollar sign. A USD 10,782.00 Wise credit showed as "+$10,782.00"
in a column of AUD figures — the same payment from the statement, one row above,
correctly showed $15,518.53 over USD 10,782.00. So the feed row read as $10,782
AUD when the real value is about $15,500, and the sub-line just repeated the
same number correctly labelled.

amount_unconverted is already selected by the transactions query (queries.ts:298)
and was simply unused here. When set, the native figure becomes the headline and
the absence of a rate is stated rather than papered over.

Pre-existing rather than Frollo's: any row with amount_aud NULL and a foreign
currency hits it, including foreign order-receipt rows. Frollo made it visible
at scale — 39 rows.

src/app/transactions/page.tsx

@@ -1059,12 +1059,33 @@ function TransactionsContent() {
                   <td className={`p-2 text-right whitespace-nowrap font-mono ${
                     SPEND_TYPES.has(t.transaction_type) ? "text-red-400" : "text-green-400"
                   }`}>
+                    {/*
+                      A row with no AUD figure must NOT be printed as AUD.
+                      `amount_aud ?? amount` formatted with the default currency
+                      rendered a USD 10,782.00 Wise credit as "+$10,782.00" in a
+                      column of AUD figures — the real value was about $15,500,
+                      and the row directly above it (the same payment from the
+                      statement) showed exactly that. The native figure is the
+                      only true one here, so it becomes the headline and the
+                      absence of a rate is stated rather than papered over.
+                    */}
+                    {t.amount_unconverted ? (
+                      <>
+                        {formatAmount(t.amount, t.transaction_type, t.currency)}
+                        <div className="text-[10px] text-zinc-500 mt-0.5" title="No AUD figure exists for this row — it is excluded from AUD totals">
+                          no AUD rate
+                        </div>
+                      </>
+                    ) : (
+                      <>
                         {formatAmount(t.amount_aud ?? t.amount, t.transaction_type)}
                         {t.currency && t.currency !== "AUD" && (
                           <div className="text-[10px] text-zinc-500 mt-0.5">
                             {formatAmount(t.amount, t.transaction_type, t.currency)}
                           </div>
                         )}
+                      </>
+                    )}
                   </td>
                   <td className="p-2">
                     <EditableTypeBadge