fix(trips): the trip form drops its complaint once you edit, and the typed date hint follows your language

"Title is required" stayed on screen after the title was typed, until the
next save. Any edit in the trip form, desktop and phone, now clears the
last save's complaint; the next save checks again.

The keyboard date field always hinted DD.MM.YYYY, while it was filled and
read back in the user's own order: a Korean user saw "2026. 12. 10." under
a German hint. The hint is now the locale's own pattern (YYYY. MM. DD. in
Korean, MM/DD/YYYY in US English), and the field's name is translated.

Refs #2604

client/src/components/shared/CustomDateTimePicker.tsx

@@ -3,6 +3,7 @@ import { localIsoDate } from '../../utils/localDate';
 import React, { useEffect, useRef, useState } from 'react';
 import { createPortal } from 'react-dom';
 import { useTranslation } from '../../i18n';
+import { dateInputPattern } from '../../utils/dateInputPattern';
 import { useRemeasureSignal } from '../../hooks/useAnchoredPosition';
 import { useWeekStartDay } from '../../hooks/useWeekStartDay';
 import { leadingBlanks, weekdayLabels } from '../../utils/calendarWeek';
@@ -276,8 +277,8 @@ export function CustomDatePicker({
             if (e.key === 'Escape') setIsTyping(false);
           }}
           onBlur={handleTextSubmit}
-          placeholder="DD.MM.YYYY"
-          aria-label="Enter date manually"
+          placeholder={dateInputPattern(locale)}
+          aria-label={t('common.datepicker.enterManually')}
           style={{
             width: '100%',
             padding: '8px 14px',