Fix imported transaction date shifts (#394)

## Summary
- format imported dates from local date parts instead of UTC ISO strings
- add regression coverage for Europe/Madrid date imports

## Tests
- npm test -- resources/js/lib/file-parser.test.ts

resources/js/lib/file-parser.test.ts

@@ -1,6 +1,10 @@
 import { DateFormat } from '@/types/import';
 import { describe, expect, it } from 'vitest';
-import { autoDetectDateFormat, getLocaleDateFormat } from './file-parser';
+import {
+    autoDetectDateFormat,
+    convertRowsToTransactions,
+    getLocaleDateFormat,
+} from './file-parser';
 
 describe('getLocaleDateFormat', () => {
     it('returns null for undefined locale', () => {
@@ -32,6 +36,37 @@ describe('getLocaleDateFormat', () => {
     });
 });
 
+describe('convertRowsToTransactions', () => {
+    it('keeps imported dates stable in timezones ahead of UTC', () => {
+        const originalTimezone = process.env.TZ;
+        process.env.TZ = 'Europe/Madrid';
+
+        try {
+            const transactions = convertRowsToTransactions(
+                [
+                    {
+                        date: '04/05/2026',
+                        description: 'Tarjeta Abril',
+                        amount: '10.00',
+                    },
+                ],
+                {
+                    transaction_date: 'date',
+                    description: 'description',
+                    amount: 'amount',
+                    balance: null,
+                },
+                DateFormat.DayMonthYear,
+            );
+
+            expect(transactions).toHaveLength(1);
+            expect(transactions[0].transaction_date).toBe('2026-05-04');
+        } finally {
+            process.env.TZ = originalTimezone;
+        }
+    });
+});
+
 describe('autoDetectDateFormat', () => {
     it('returns null for empty data', () => {
         expect(autoDetectDateFormat([], 'date')).toBeNull();

resources/js/lib/file-parser.ts

@@ -447,6 +447,14 @@ export function parseDate(
     return date;
 }
 
+function formatLocalDate(date: Date): string {
+    const year = date.getFullYear();
+    const month = String(date.getMonth() + 1).padStart(2, '0');
+    const day = String(date.getDate()).padStart(2, '0');
+
+    return `${year}-${month}-${day}`;
+}
+
 export function parseAmount(amountStr: string | number): number | null {
     if (typeof amountStr === 'number') {
         return amountStr;
@@ -572,7 +580,7 @@ export function convertRowsToTransactions(
             continue;
         }
 
-        const formattedDate = date.toISOString().split('T')[0];
+        const formattedDate = formatLocalDate(date);
 
         let balance: number | null = null;
         if (mapping.balance && row[mapping.balance]) {