extend chat model with CRUD actions for event changes

- Add ProposedEventChange type with create/update/delete actions
- Replace proposedEvent with proposedChange in ChatMessage
- Add currentDate to AIContext for time-aware AI responses
- Add AI test endpoint for development (/api/ai/test)
- Fix MongoUserRepository type safety with explicit toUser mapping
- Update CLAUDE.md documentation

apps/server/src/services/interfaces/AIProvider.ts

@@ -1,14 +1,15 @@
-import { CalendarEvent, ChatMessage, CreateEventDTO } from '@caldav/shared';
+import { CalendarEvent, ChatMessage, ProposedEventChange } from '@caldav/shared';
 
 export interface AIContext {
   userId: string;
   conversationHistory: ChatMessage[];
   existingEvents: CalendarEvent[];
+  currentDate: Date;
 }
 
 export interface AIResponse {
   content: string;
-  proposedEvent?: CreateEventDTO;
+  proposedChange?: ProposedEventChange;
 }
 
 export interface AIProvider {