feat(agents): add multi-agent supervisor primitives

[tikhandesanket]

Description

This PR implements the multi-agent supervisor pattern proposed in #289.

The supervisor acts as a central orchestrator that receives a user request, determines which specialist agent should handle it, and routes the request accordingly.

The implementation focuses on keeping the agents decoupled, with the supervisor responsible for coordination rather than embedding specialist-specific logic into individual agents.

Related issue

Fixes #289

Changes

• Add a supervisor agent responsible for routing requests.
• Support routing to multiple specialist agents.
• Preserve conversation/state information during agent handoffs.
• Keep specialist agents independently defined and reusable.
• Add tests covering supervisor routing and agent handoffs.

Testing

• Tests pass locally
• Ruff checks pass
• Documentation updated, if applicable

Checklist

• My changes are focused and relevant to this pull request.
• I have added or updated tests where appropriate.
• I have reviewed my changes for unrelated modifications.
• I have updated documentation where necessary.