feat: session state serialization (Pause/Resume)

[rosspeili]

Problem Statement

If a user exits the terminal or the process is interrupted, the entire state of a multi-turn session is lost. There is currently no way to "pause" a long-running debate and resume it later with the exact same agent states, history, and configuration.

Proposed Solution

1. Implement to_dict() and from_dict() methods for the Session class in session.py.
2. This should capture the full SessionConfig, the state of all Agent instances, the entire conversation history, and metadata like turn_count.
3. Add a CLI command or a post-session option to "Save Snapshot" which writes this state to a JSON file.
4. Update the CLI wizard to allow "Resuming from Snapshot" by loading one of these JSON files.

Alternatives Considered

Database-backed persistence, but JSON serialization matches our current local-first, file-based storage philosophy.

Priority

Low 🟢

Additional Context

Crucial for complex projects, multi-day simulations, or research tasks that span more than one sitting.