feat: add recurring event deletion with three modes

Implement three deletion modes for recurring events:
- single: exclude specific occurrence via EXDATE mechanism
- future: set RRULE UNTIL to stop future occurrences
- all: delete entire event series

Changes include:
- Add exceptionDates field to CalendarEvent model
- Add RecurringDeleteMode type and DeleteRecurringEventDTO
- EventService.deleteRecurring() with mode-based logic using rrule library
- EventController DELETE endpoint accepts mode/occurrenceDate query params
- recurrenceExpander filters out exception dates during expansion
- AI tools support deleteMode and occurrenceDate for proposed deletions
- ChatService.confirmEvent() handles recurring delete modes
- New DeleteEventModal component for unified delete confirmation UI
- Calendar screen integrates modal for both recurring and non-recurring events

apps/client/src/services/ChatService.ts

@@ -7,6 +7,7 @@ import {
   CreateEventDTO,
   UpdateEventDTO,
   EventAction,
+  RecurringDeleteMode,
 } from "@calchat/shared";
 import { ApiClient } from "./ApiClient";
 
@@ -16,6 +17,8 @@ interface ConfirmEventRequest {
   event?: CreateEventDTO;
   eventId?: string;
   updates?: UpdateEventDTO;
+  deleteMode?: RecurringDeleteMode;
+  occurrenceDate?: string;
 }
 
 interface RejectEventRequest {
@@ -35,6 +38,8 @@ export const ChatService = {
     event?: CreateEventDTO,
     eventId?: string,
     updates?: UpdateEventDTO,
+    deleteMode?: RecurringDeleteMode,
+    occurrenceDate?: string,
   ): Promise<ChatResponse> => {
     const body: ConfirmEventRequest = {
       proposalId,
@@ -42,6 +47,8 @@ export const ChatService = {
       event,
       eventId,
       updates,
+      deleteMode,
+      occurrenceDate,
     };
     return ApiClient.post<ChatResponse>(
       `/chat/confirm/${conversationId}/${messageId}`,