Updated to the latest Vaadin and Langchain4j Versions

[SebastianKuehnau]

This commit updates the OpenAI configuration, switches the model to gpt-5, and introduces an adjustable temperature for response diversity. Dependencies have been modernized (including Vaadin, LangChain, and Spring Boot), laying the foundation for new features. Document processing recursively loads content from directories. The chat view has been redesigned: real streaming responses with continuous updating, automatic scrolling, improved styling.