add event CRUD actions and recurring event expansion

- Implement full CRUD in MongoEventRepository (findById, findByUserId, findByDateRange, update, delete)
- Extend ChatService to handle create/update/delete actions with dynamic test responses
- Add recurrenceExpander utility using rrule library for RRULE parsing
- Add eventFormatters utility for German-localized week/month overviews
- Add German translations for days and months in shared Constants
- Update client ChatService to support all event actions (action, eventId, updates params)

packages/shared/src/models/Constants.ts

@@ -37,3 +37,42 @@ export const DAY_INDEX: Record<Day, number> = {
   Friday: 5,
   Saturday: 6,
 };
+
+// Mapping from Date.getDay() index (0=Sunday) to Day type
+export const DAY_INDEX_TO_DAY: Day[] = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];
+
+// German translations
+export const DAY_TO_GERMAN: Record<Day, string> = {
+  Monday: 'Montag',
+  Tuesday: 'Dienstag',
+  Wednesday: 'Mittwoch',
+  Thursday: 'Donnerstag',
+  Friday: 'Freitag',
+  Saturday: 'Samstag',
+  Sunday: 'Sonntag',
+};
+
+export const DAY_TO_GERMAN_SHORT: Record<Day, string> = {
+  Monday: 'Mo',
+  Tuesday: 'Di',
+  Wednesday: 'Mi',
+  Thursday: 'Do',
+  Friday: 'Fr',
+  Saturday: 'Sa',
+  Sunday: 'So',
+};
+
+export const MONTH_TO_GERMAN: Record<Month, string> = {
+  January: 'Januar',
+  February: 'Februar',
+  March: 'März',
+  April: 'April',
+  May: 'Mai',
+  June: 'Juni',
+  July: 'Juli',
+  August: 'August',
+  September: 'September',
+  October: 'Oktober',
+  November: 'November',
+  December: 'Dezember',
+};