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)

apps/server/src/utils/eventFormatters.ts

@@ -0,0 +1,125 @@
+import {
+  MONTHS,
+  DAY_INDEX_TO_DAY,
+  DAY_TO_GERMAN,
+  DAY_TO_GERMAN_SHORT,
+  MONTH_TO_GERMAN,
+} from '@caldav/shared';
+import { EventRepository } from '../services/interfaces';
+import { expandRecurringEvents, ExpandedEvent } from './recurrenceExpander';
+
+// Private formatting helpers
+
+function formatTime(date: Date): string {
+  const hours = date.getHours().toString().padStart(2, '0');
+  const minutes = date.getMinutes().toString().padStart(2, '0');
+  return `${hours}:${minutes}`;
+}
+
+function formatDateShort(date: Date): string {
+  const day = date.getDate().toString().padStart(2, '0');
+  const month = (date.getMonth() + 1).toString().padStart(2, '0');
+  return `${day}.${month}.`;
+}
+
+function getWeekNumber(date: Date): number {
+  const d = new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()));
+  const dayNum = d.getUTCDay() || 7;
+  d.setUTCDate(d.getUTCDate() + 4 - dayNum);
+  const yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
+  return Math.ceil((((d.getTime() - yearStart.getTime()) / 86400000) + 1) / 7);
+}
+
+function formatWeeksText(events: ExpandedEvent[], weeks: number): string {
+  const weeksText = weeks === 1 ? 'die nächste Woche' : `die nächsten ${weeks} Wochen`;
+
+  if (events.length === 0) {
+    return `Du hast für ${weeksText} keine Termine.`;
+  }
+
+  const lines: string[] = [`Hier sind deine Termine für ${weeksText}:\n`];
+
+  for (const event of events) {
+    const day = DAY_INDEX_TO_DAY[event.occurrenceStart.getDay()];
+    const weekday = DAY_TO_GERMAN[day];
+    const dateStr = formatDateShort(event.occurrenceStart);
+    const timeStr = formatTime(event.occurrenceStart);
+    lines.push(`${weekday}, ${dateStr} - ${timeStr} Uhr: ${event.title}`);
+  }
+
+  lines.push(`\nInsgesamt ${events.length} Termin${events.length === 1 ? '' : 'e'}.`);
+  return lines.join('\n');
+}
+
+function formatMonthText(events: ExpandedEvent[], monthName: string): string {
+  if (events.length === 0) {
+    return `Du hast im ${monthName} keine Termine.`;
+  }
+
+  // Group events by calendar week
+  const weekGroups = new Map<number, ExpandedEvent[]>();
+  for (const event of events) {
+    const weekNum = getWeekNumber(event.occurrenceStart);
+    if (!weekGroups.has(weekNum)) {
+      weekGroups.set(weekNum, []);
+    }
+    weekGroups.get(weekNum)!.push(event);
+  }
+
+  const lines: string[] = [`Hier ist deine Monatsübersicht für ${monthName}:\n`];
+
+  // Sort weeks and format
+  const sortedWeeks = Array.from(weekGroups.keys()).sort((a, b) => a - b);
+  for (const weekNum of sortedWeeks) {
+    const weekEvents = weekGroups.get(weekNum)!;
+    lines.push(`KW ${weekNum}: ${weekEvents.length} Termin${weekEvents.length === 1 ? '' : 'e'}`);
+
+    for (const event of weekEvents) {
+      const day = DAY_INDEX_TO_DAY[event.occurrenceStart.getDay()];
+      const weekdayShort = DAY_TO_GERMAN_SHORT[day];
+      const dateStr = formatDateShort(event.occurrenceStart);
+      const timeStr = formatTime(event.occurrenceStart);
+      lines.push(`  • ${weekdayShort} ${dateStr}, ${timeStr}: ${event.title}`);
+    }
+    lines.push('');
+  }
+
+  lines.push(`Insgesamt ${events.length} Termin${events.length === 1 ? '' : 'e'} im ${monthName}.`);
+  return lines.join('\n');
+}
+
+// Public API
+
+/**
+ * Get a formatted overview of events for the next x weeks.
+ * Recurring events are expanded to show all occurrences within the range.
+ */
+export async function getWeeksOverview(
+  eventRepo: EventRepository,
+  userId: string,
+  weeks: number
+): Promise<string> {
+  const now = new Date();
+  const endDate = new Date(now.getTime() + weeks * 7 * 24 * 60 * 60 * 1000);
+  const events = await eventRepo.findByUserId(userId);
+  const expanded = expandRecurringEvents(events, now, endDate);
+  return formatWeeksText(expanded, weeks);
+}
+
+/**
+ * Get a formatted overview of events for a specific month.
+ * Recurring events are expanded to show all occurrences within the month.
+ */
+export async function getMonthOverview(
+  eventRepo: EventRepository,
+  userId: string,
+  year: number,
+  month: number
+): Promise<string> {
+  const startOfMonth = new Date(year, month, 1);
+  const endOfMonth = new Date(year, month + 1, 0, 23, 59, 59);
+  const events = await eventRepo.findByUserId(userId);
+  const expanded = expandRecurringEvents(events, startOfMonth, endOfMonth);
+  const monthName = MONTH_TO_GERMAN[MONTHS[month]];
+  return formatMonthText(expanded, monthName);
+}