Add usage metrics #121

Describe the feature or problem you'd like to solve

Add command that shows sessions metrics like duration, cost, API calls, tokens, etc.

Proposed solution

It would be helpful to have access to metrics like session duration, cumulative activity duration (time the agent is doing work), number of code changes, tokens used, cost, API call count, tasks completed, or even how cost saving are achieved like one competing product has. The objective is to provide developers a clear view of spend and efficacy. My current context is a comparison of the various CLI coding agents so I need consistent data across the products but as an engineering leader I'd want to measure the value of my investment over time.

Example prompts or workflows

Add a command like "/metrics" that outputs a formatted view of the various metrics. Also, output the metrics when the CLI agent exits.

Additional context

No response