Expose reasoning effort level in status line data

Request

Add the current reasoning effort level (e.g., low, medium, high, or the extended thinking toggle state) to the JSON data sent to the status line script.

Motivation

Users who toggle between reasoning modes (via /think, --reasoning_effort, or the model picker) have no way to see the current reasoning configuration at a glance. The status line already exposes model.id, model.display_name, cost, context window stats, and other session metadata -- but reasoning effort is missing.

This is especially useful when switching between modes frequently during a session, as it's easy to lose track of the current setting.

Suggested fields

{
  "reasoning": {
    "effort": "high",
    "thinking_enabled": true
  }
}

Or any equivalent representation that surfaces the current reasoning configuration to the status line script.