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/AIProvider.ts

@@ -0,0 +1,16 @@
+import { CalendarEvent, ChatMessage, CreateEventDTO } from '@caldav/shared';
+
+export interface AIContext {
+  userId: string;
+  conversationHistory: ChatMessage[];
+  existingEvents: CalendarEvent[];
+}
+
+export interface AIResponse {
+  content: string;
+  proposedEvent?: CreateEventDTO;
+}
+
+export interface AIProvider {
+  processMessage(message: string, context: AIContext): Promise<AIResponse>;
+}