Expose rate limit / usage quota info in statusLine JSON input

Feature Request

Is your feature request related to a problem?
Yes. The statusLine command receives JSON input with context window stats, model info, session cost, etc. However, there is no way to display how close you are to hitting the 5-hour rate limit / usage quota. As a heavy user, I would like to see tokens remaining before rate limiting kicks in, directly in my status line.

Describe the solution you would like
Add rate limit / usage quota fields to the JSON input passed to the statusLine command. Something like:

{
  "rate_limit": {
    "remaining_tokens": 500000,
    "total_tokens": 1000000,
    "reset_at": "2026-02-06T22:00:00Z",
    "used_percentage": 50
  }
}

This would allow users to build status line displays that show how close they are to their usage cap.

Describe alternatives you've considered

• Using cost.total_cost_usd as a rough proxy - but this only tracks the current session and does not reflect the actual rate limit window
• Manually tracking usage externally - cumbersome and inaccurate

Additional context
The current context_window fields are great for tracking conversation context usage, but the rate limit is a separate server-side concern that would be very useful to surface in the UI. This is especially valuable for users on usage-capped plans who want to pace their work.