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

docs/architecture-class-diagram.puml

@@ -38,7 +38,7 @@ package "Controller Layer" #ADD8E6 {
 }
 
 package "Service Layer" #90EE90 {
-    package "Interfaces" {
+    package "Data Access Interfaces" {
         interface AIProvider {
             ' +processMessage()
         }
@@ -94,7 +94,7 @@ package "AI Layer" #FFA07A {
     }
 }
 
-package "Data Access Layer" #FFD700 {
+package "Data Access Implementations" #FFD700 {
     class MongoUserRepository implements UserRepository {
         ' -model: UserModel
     }