Feature: Expose account usage/quota data to statusline

Summary

It would be helpful to have account-level usage data available in the statusline JSON context, so users can see their quota usage without leaving the terminal.

Current Behavior

The statusline JSON currently includes session-level data:

"cost": {
  "total_cost_usd": 1.73,
  "total_duration_ms": 877928,
  ...
}

Requested Enhancement

Add account-level usage information:

"account": {
  "usage_usd": 45.20,
  "limit_usd": 100.00,
  "usage_percentage": 45.2,
  "resets_at": "2026-02-04T00:00:00Z",
  "period": "daily"  // or "monthly"
}

Use Case

Users who have custom statuslines can display their quota usage directly in the terminal, avoiding the need to check the Anthropic console website to monitor usage limits.

Example statusline output:

Opus 4.5 | [####-------] 45% | $45/$100 | resets in 3h

Additional Context

This would be particularly useful for users on rate-limited plans who want to pace their usage throughout the day/month.