fix(panel): double negative sign on transaction amounts

formatAmount now strips the sign since the renderer already prepends
+/- based on TYPE_CONFIG. Raw DB values like "-180" were getting a
second "-" prefix, showing as "--180".

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

panel/src/pages/Transactions.tsx

@@ -63,7 +63,8 @@ const PAGE_SIZES = [25, 50, 100];
 
 function formatAmount(amount: string): string {
   const n = BigInt(amount);
-  return n.toLocaleString();
+  const abs = n < 0n ? -n : n;
+  return abs.toLocaleString();
 }
 
 function formatDate(iso: string): string {