[Feature Request] Expose subscription quota usage in statusline JSON

Description

It would be useful to have subscription rate limit / quota data available in the statusline JSON input, so users can display how many tokens they have remaining in their 5-hour usage window.

Current behavior

The statusline JSON currently exposes:

• context_window.used_percentage
• cost.total_cost_usd
• cost.total_duration_ms
• model.display_name
• workspace.current_dir

There is no data about subscription quota usage or rate limits.

Proposed addition

Add fields such as:

• quota.used_percentage — percentage of 5-hour window quota consumed
• quota.remaining_tokens — tokens remaining in the current window
• quota.window_reset_at — timestamp when the usage window resets

This would allow users to build a visual indicator (e.g., a progress bar) in their custom statusline showing how much of their subscription quota remains.

Use case

Subscription users currently have no visibility into how close they are to hitting their 5-hour rate limit until they actually get throttled. Surfacing this data in the statusline would help users pace their usage and avoid unexpected throttling.