feat(MiniCalendarWidget): enhance localization and refactor calendar logic

- Updated the MiniCalendarWidget to utilize localized strings for month names, weekdays, and loading messages, improving user experience across multiple languages.
- Refactored the calendar logic to use constants for month keys and weekday order, ensuring consistency with backend configurations.
- Added new translation entries for the mini widget in Cebuano, German, English, Spanish, and French, enhancing accessibility for users.

frontend/src/i18n/locales/de/personal.json

@@ -49,6 +49,10 @@
                 "nov": "November",
                 "dec": "Dezember"
             },
+            "miniWidget": {
+                "loading": "Kalender wird geladen…",
+                "linkToCalendar": "Zum Kalender →"
+            },
             "categories": {
                 "personal": "Persönlich",
                 "work": "Arbeit",