fix(currency): show and settle foreign transactions in AUD

The transactions page rendered the statement's native amount through a
formatter hardcoded to AUD, so a USD row displayed its USD figure labelled as
dollars while every analytics query counted the converted amount_aud. Same
transaction, two different numbers depending on the page.

getTransactions now returns the statement currency, the amount column shows
amount_aud with the native figure beneath it when the two differ, and the split
and duplicate modals seed from the converted amount (a duplicate becomes a
manual AUD row, so the native figure would be wrong there).

Settlement balances had the same split: getParticipantBalances and the
per-participant balance route summed raw amount while trip totals summed
amount_aud, so a shared foreign expense would net a USD figure against AUD
ones. All three now agree on amount_aud. No change to current balances - every
statement in the database is AUD today - but correct once Wise data lands.

src/lib/queries.ts

@@ -34,6 +34,9 @@ export interface TransactionRow {
   effective_merchant: string;
   // statement context (null for manual transactions)
   bank_name: string;
+  // Native currency of the statement this row came from ('AUD' for manual rows).
+  // `amount` is in this currency; `amount_aud` is the converted figure.
+  currency: string;
   owner_id: number;
   owner_name: string;
   // tags
@@ -198,6 +201,7 @@ export async function getTransactions(ownerId: number, filters: TransactionFilte
       COALESCE(o.category_override, t.category) as effective_category,
       COALESCE(o.merchant_normalized, t.merchant_normalized, t.merchant_name) as effective_merchant,
       COALESCE(s.bank_name, 'Manual') as bank_name,
+      COALESCE(s.currency, 'AUD') as currency,
       COALESCE(t.owner_id, s.owner_id) as owner_id,
       p.name as owner_name,
       COALESCE(src.created_at, t.created_at) as created_at,
@@ -362,8 +366,10 @@ export async function getParticipantBalances(ownerId: number, tagIds?: number[])
 
     LEFT JOIN (
       -- They owe me: their splits on transactions I own
+      -- Settle in AUD: on a foreign-currency row the amount column is in its own
+      -- currency, so splitting on it nets a USD figure against AUD ones.
       SELECT ts.participant_id AS pid,
-        (CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN t.amount ELSE -t.amount END) * ts.share_percent / 100 AS signed_amount,
+        (CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN COALESCE(t.amount_aud, t.amount) ELSE -COALESCE(t.amount_aud, t.amount) END) * ts.share_percent / 100 AS signed_amount,
         1 AS split_count
       FROM transaction_splits ts
       JOIN transactions t ON t.id = ts.transaction_id
@@ -376,7 +382,7 @@ export async function getParticipantBalances(ownerId: number, tagIds?: number[])
 
       -- I owe them: my splits on transactions they own
       SELECT COALESCE(t.owner_id, s.owner_id) AS pid,
-        -((CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN t.amount ELSE -t.amount END) * ts.share_percent / 100) AS signed_amount,
+        -((CASE WHEN t.transaction_type IN ('debit', 'fee', 'interest') THEN COALESCE(t.amount_aud, t.amount) ELSE -COALESCE(t.amount_aud, t.amount) END) * ts.share_percent / 100) AS signed_amount,
         0 AS split_count
       FROM transaction_splits ts
       JOIN transactions t ON t.id = ts.transaction_id