Langchain4j Spring Boot Integration

This brings LangChain4j into Spring Boot with auto-configuration and declarative AI services through interface annotations. You define an interface with @AiService, add message templates, and Spring's dependency injection handles the rest. It covers the full stack: configuring model beans through application.properties, setting up chat memory with @MemoryId, wiring RAG pipelines with Spring Data embedding stores, and exposing tools as @Component beans. The property-based configuration is clean, but you'll likely need manual bean definitions once you're juggling multiple providers or custom retry logic. Good fit if you're already deep in the Spring ecosystem and want AI services that feel like any other autowired bean.