Include reasoning effort level in statusline JSON data

Feature Request

The statusline script receives JSON data via stdin with fields like model, context_window, workspace, etc. However, the current reasoning effort level (auto/low/medium/high/max) is not included in this payload.

Problem

Users who want to display the current effort level in their custom statusline have no reliable way to do so. The only workaround is reading alwaysThinkingEnabled from settings.json, which only gives a boolean and doesn't reflect the actual effort level (e.g., "auto (currently medium)").

Proposed Solution

Add an effort or reasoning_effort field to the statusline JSON, e.g.:

{
  "reasoning_effort": {
    "setting": "auto",
    "current": "medium"
  }
}

This would allow statusline scripts to accurately display the current effort level alongside model and context info.

Context

The effort level is already visible in Claude Code's built-in right-side status indicator, but users customizing the left-side statusline via statusline in settings cannot access this value.