[Feature Request] Add plan usage/quota variables to status line for MAX subscribers

Question

**Bug Description**
Feature Request: Show MAX plan usage/quota in status line

Currently, the status line API exposes `total_cost_usd` for API usage, but for MAX subscribers, this doesn't reflect our actual plan quota.

Request: Please add variables like:
  - `plan.usage_remaining` or `plan.tokens_remaining`
  - `plan.usage_percentage`
  - `plan.quota_limit`

This would allow MAX subscribers to monitor their usage directly in the status line without leaving the terminal.

**Environment Inf