implement backend skeleton with MongoDB and Claude AI integration

- Add controllers (Auth, Chat, Event) with placeholder implementations
- Add services (Auth, Chat, Event) with business logic interfaces
- Add repositories with MongoDB/Mongoose models (User, Event, Chat)
- Add middleware for JWT authentication
- Add Claude AI adapter implementing AIProvider interface
- Add utility modules for JWT and password handling
- Add shared types and DTOs for User, CalendarEvent, ChatMessage
- Configure routes with proper endpoint structure
- Update app.ts with dependency injection setup
- Add required dependencies: mongoose, bcrypt, jsonwebtoken, @anthropic-ai/sdk

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

@@ -0,0 +1,11 @@
+import { ChatMessage, Conversation, CreateMessageDTO, GetMessagesOptions } from '@caldav/shared';
+
+export interface ChatRepository {
+  // Conversations
+  getConversationsByUser(userId: string): Promise<Conversation[]>;
+  createConversation(userId: string): Promise<Conversation>;
+
+  // Messages (cursor-based pagination)
+  getMessages(conversationId: string, options?: GetMessagesOptions): Promise<ChatMessage[]>;
+  createMessage(conversationId: string, message: CreateMessageDTO): Promise<ChatMessage>;
+}