Implement native LLM agent integration

[Artmann]

Provide full native support for LLM agents (Cursor, Windsurf, etc.) to interact with .deepnote files programmatically, enabling agents to read, modify, and execute notebooks.

• Expose notebook structure to agents (cells, outputs, dependencies)
• Allow agents to modify notebook content
• Support execution requests from agents
• Stream execution results back to agents
• Provide context aboutthe environment and dependencies