Optional session activity indicators and unread result markers #14

The chat history uses the same icon for every conversation, so it is difficult to see which agents are working, need input, or have produced a result that has not yet been opened.

Following CONTRIBUTING.md's request to discuss substantial features, I am proposing an opt-in setting that preserves the existing visual design by default:

• Live activity, blocking input/approval waits, and unanswered non-blocking questions.
• Green markers for new results, cleared only after a successful open through Codex Extras; a later completion becomes green again.
• Small gray dots for reviewed, idle, and unknown states to preserve alignment.

An implementation is ready for review. It observes the official Codex extension's internal local IPC and explicit lifecycle records in bounded session-log tails, without polling for status or starting another app-server. This internal protocol is undocumented, so the setting is experimental and disabled by default. Connection loss invalidates activity; a connected but frozen owner cannot be reliably detected. Live connectivity has been checked on Windows; Linux tests use a mocked transport.

This feature is independent of the archive filtering fix in #13. No extension version bump is proposed.