Feature Request: Expose plan usage/subscription limits in status line input

Summary

The current_usage field added in v2.0.70 is great for showing context window percentage in custom status lines. It would be valuable to also expose plan/subscription usage data (daily/weekly Opus/Sonnet limits) in the status line JSON input.

Use Case

Users with custom status lines (via /statusline) can now display context window usage thanks to current_usage. However, there's no way to show subscription limit usage (what /usage displays) without calling an external API.

Being able to see "X% of daily Opus limit used" alongside context window usage would help users manage their usage more effectively without needing to run /usage repeatedly.

Suggested Fields

Add to status line input JSON:

{
  "plan_usage": {
    "opus": {
      "used_percent": 45,
      "limit_type": "daily"
    },
    "sonnet": {
      "used_percent": 12,
      "limit_type": "daily"
    }
  }
}

Or similar structure that exposes the data shown by /usage.

Context

• v2.0.70 added current_usage for context window tracking
• Custom status lines are configured via /statusline command
• Plan usage is currently only visible via /usage command