Tasa Cero: badges, convert dialog, Financiamientos page

Violet 'Tasa Cero'/'Cuota' badges (anchor amount struck through like
deferred), convert/edit action on CC purchases with a live cuota
preview, and a Financiamientos page mirroring the bank's tab (progress,
monto cuota, saldo inicial/faltante, totals).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/pages/Budget.tsx

@@ -14,6 +14,7 @@ import PeriodNavigator from '@/components/PeriodNavigator';
 import MonthlyDetail from '@/components/budget/MonthlyDetail';
 import RecurringItemsManager from '@/components/budget/RecurringItemsManager';
 import TransactionList from '@/components/TransactionList';
+import ConvertToInstallmentsDialog from '@/components/transactions/ConvertToInstallmentsDialog';
 
 
 const MIN_YEAR = 2026;
@@ -44,6 +45,7 @@ export default function Budget() {
   const [subTab, setSubTab] = useState<'detail' | 'transactions'>('detail');
   const [txSearch, setTxSearch] = useState('');
   const [txSource, setTxSource] = useState<'CREDIT_CARD' | 'CASH_AND_TRANSFER'>('CREDIT_CARD');
+  const [convertTx, setConvertTx] = useState<Transaction | null>(null);
 
   const txQuery = useQuery({
     queryKey: ['transactions', 'budget', year, selectedMonth, txSource, txSearch],
@@ -79,6 +81,7 @@ export default function Budget() {
 
   const invalidateTransactionsAndBudget = useCallback(() => {
     queryClient.invalidateQueries({ queryKey: ['transactions'] });
+    queryClient.invalidateQueries({ queryKey: ['installment-plans'] });
     refresh();
   }, [queryClient, refresh]);
 
@@ -209,6 +212,7 @@ export default function Budget() {
                 showSourceIcon={txSource === 'CASH_AND_TRANSFER'}
                 emptyMessage={`Sin transacciones de ${txSource === 'CREDIT_CARD' ? 'tarjeta' : 'efectivo o transferencia'} en ${MONTH_NAMES[selectedMonth]}`}
                 onToggleDeferred={txSource === 'CREDIT_CARD' ? handleToggleDeferred : undefined}
+                onConvertTasaCero={txSource === 'CREDIT_CARD' ? setConvertTx : undefined}
               />
               )}
             </TabsContent>
@@ -224,6 +228,13 @@ export default function Budget() {
           />
         </TabsContent>
       </Tabs>
+
+      <ConvertToInstallmentsDialog
+        open={convertTx !== null}
+        onOpenChange={(open) => !open && setConvertTx(null)}
+        onSaved={invalidateTransactionsAndBudget}
+        tx={convertTx}
+      />
     </div>
   );
 }