Add a user-selectable date format (e.g. dd.mm.yyyy for European/German locales)

📑 I have found these related issues/pull requests I checked and found a related issue ([#4584]( but no request specific to this case. 🔖 Feature description Uptime Kuma currently displays dates in a fixed format (e.g. yyyy.mm.dd), which follows a US-style convention. In most of Europe, including Germany, the standard order is day.month.year (dd.mm.yyyy). Because the two formats look similar but order the day/month differently, this can genuinely confuse users when the day is ≤ 12 (e.g. 03.04.2026 could mean March 4th or April 3rd). ✔️ Solution Add a date format setting (e.g. under Settings > Appearance) letting users pick between common formats such as: • dd.mm.yyyy • mm.dd.yyyy • yyyy-mm-dd This feature should be selectable regardless of the selected language. ❓ Alternatives Alternatively, derive the format automatically from the browser's locale (Intl.DateTimeFormat / vue-i18n) instead of a hardcoded dayjs.format() string, this would also resolve th…