Feature: Expose hourly rate limit / usage percentage in status line data

Feature Request

Problem

The status line JSON data currently exposes session cost (cost.total_cost_usd) and context window usage (context_window.used_percentage), but there's no way to see how much of your hourly API rate limit has been consumed.

For users on plans with hourly usage caps (e.g., Max plan), knowing how much of the hourly window remains is critical for pacing work and avoiding unexpected throttling mid-task.

Proposed Solution

Add rate limit fields to the status line JSON, for example:

{
  "rate_limit": {
    "used_percentage": 62,
    "remaining_percentage": 38,
    "resets_at": "2026-02-26T15:00:00Z"
  }
}

This would allow custom status line scripts to display usage alongside context % and cost, e.g.:

transfix (ES-1234-feature)  Opus  [██████░░░░] 62%  $0.23  ⏱ 62% hourly

Alternatives Considered

• Custom hooks: A PostToolUse hook could track request counts, but it can't access the actual API quota or know the cap.
• /cost command: Shows session stats interactively but doesn't integrate into the status line for at-a-glance monitoring.

Additional Context

The status line is already a great place for at-a-glance session health. Adding rate limit info would make it a complete picture — context, cost, and capacity.