Refactor: Integrate advanced memory system into chat agent

[basnijholt]

Currently, the 'chat' agent uses a simple JSON-based memory system (defined in agent_cli/_tools.py). It should be refactored to use the advanced, vector-backed memory system provided by the 'memory' command (agent_cli/memory/) for better retrieval and scalability.

[basnijholt]

Closing as this was a test issue created during documentation review.

[basnijholt]

Reopening as this is a valid refactoring task identified during review.