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/UserRepository.ts

@@ -0,0 +1,13 @@
+import { User } from '@caldav/shared';
+
+export interface CreateUserData {
+  email: string;
+  displayName: string;
+  passwordHash: string;
+}
+
+export interface UserRepository {
+  findById(id: string): Promise<User | null>;
+  findByEmail(email: string): Promise<User | null>;
+  create(data: CreateUserData): Promise<User>;
+}