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/client/src/app/(tabs)/chat.tsx

@@ -5,7 +5,7 @@ import Header from "../../components/Header";
 import BaseBackground from "../../components/BaseBackground";
 import { FlashList } from "@shopify/flash-list";
 import { ChatService } from "../../services";
-import { ProposedEventChange, CreateEventDTO } from "@caldav/shared";
+import { ProposedEventChange } from "@caldav/shared";
 import { ProposedEventCard } from "../../components/ProposedEventCard";
 
 // TODO: better shadows for everything
@@ -40,7 +40,7 @@ const Chat = () => {
     action: "confirm" | "reject",
     messageId: string,
     conversationId: string,
-    event?: CreateEventDTO
+    proposedChange?: ProposedEventChange
   ) => {
     // Mark message as responded (optimistic update)
     setMessages((prev) =>
@@ -51,8 +51,15 @@ const Chat = () => {
 
     try {
       const response =
-        action === "confirm" && event
-          ? await ChatService.confirmEvent(conversationId, messageId, event)
+        action === "confirm" && proposedChange
+          ? await ChatService.confirmEvent(
+              conversationId,
+              messageId,
+              proposedChange.action,
+              proposedChange.event,
+              proposedChange.eventId,
+              proposedChange.updates
+            )
           : await ChatService.rejectEvent(conversationId, messageId);
 
       const botMessage: MessageData = {
@@ -112,7 +119,7 @@ const Chat = () => {
             proposedChange={item.proposedChange}
             respondedAction={item.respondedAction}
             onConfirm={() =>
-              handleEventResponse("confirm", item.id, item.conversationId!, item.proposedChange?.event)
+              handleEventResponse("confirm", item.id, item.conversationId!, item.proposedChange)
             }
             onReject={() =>
               handleEventResponse("reject", item.id, item.conversationId!)

apps/client/src/services/ChatService.ts

@@ -5,9 +5,18 @@ import {
   ConversationSummary,
   GetMessagesOptions,
   CreateEventDTO,
+  UpdateEventDTO,
+  EventAction,
 } from "@caldav/shared";
 import { ApiClient } from "./ApiClient";
 
+interface ConfirmEventRequest {
+  action: EventAction;
+  event?: CreateEventDTO;
+  eventId?: string;
+  updates?: UpdateEventDTO;
+}
+
 export const ChatService = {
   sendMessage: async (data: SendMessageDTO): Promise<ChatResponse> => {
     return ApiClient.post<ChatResponse>("/chat/message", data);
@@ -16,9 +25,13 @@ export const ChatService = {
   confirmEvent: async (
     conversationId: string,
     messageId: string,
-    event: CreateEventDTO
+    action: EventAction,
+    event?: CreateEventDTO,
+    eventId?: string,
+    updates?: UpdateEventDTO
   ): Promise<ChatResponse> => {
-    return ApiClient.post<ChatResponse>(`/chat/confirm/${conversationId}/${messageId}`, event);
+    const body: ConfirmEventRequest = { action, event, eventId, updates };
+    return ApiClient.post<ChatResponse>(`/chat/confirm/${conversationId}/${messageId}`, body);
   },
 
   rejectEvent: async (