[Roadmap] Implement 'Projects' (like Claude) feature to enhance organization and context

Why Users will be able to create and manage structured workspaces within Big-AGI for maintaining contextual data across interactions, improving productivity and focus when working on specific tasks or projects.

Description Implement a "Projects" feature similar to Claude Projects, where users can organize their work into self-contained workspaces. Each workspace will store documents, chat history, and contextual instructions, enabling Big-AGI to provide tailored responses.