Add BaseService and refactor ChatService for improved dependency management

- Introduce BaseService as a foundational class for services, providing standardized dependency injection and initialization logic.
- Refactor ChatService to extend BaseService, enhancing its initialization process and dependency handling.
- Implement service metadata and structured initialization in ChatService, allowing for better tracking and error handling during service setup.
- Update chat module to initialize ChatService with dependency management, ensuring readiness before use.

src/core/di-container.ts

@@ -1,5 +1,7 @@
 import type { DIContainer, ServiceToken } from './types'
 
+export type { ServiceToken } from './types'
+
 interface ServiceRegistration {
   service: any
   scope: 'singleton' | 'transient'