Add persistent setting to always show thinking trace

Feature Request

Currently, the only way to view the thinking/reasoning trace in Claude Code is by toggling verbose mode with Ctrl+O during a session. This toggle resets every session — there is no way to make it persistent.

Requested Change

Add a setting (e.g. "alwaysShowThinking": true) in settings.json (both global ~/.claude/settings.json and project-level) that enables verbose/thinking trace display by default, so users don't have to press Ctrl+O at the start of every session.

Motivation

• Users who work with effortLevel: "high" want to see the reasoning trace consistently — it's part of their workflow, not an occasional debug toggle.
• Having to remember to press Ctrl+O every session is friction that a one-time config should eliminate.
• Every other thinking-related setting (effortLevel, model) is already persistable in settings.json; the display toggle should be too.

Proposed Behavior

| Setting | Default | Effect |
|---------|---------|--------|
| "showThinking": true | false | Thinking trace is displayed by default when a session starts (equivalent to Ctrl+O being pre-toggled on) |

Ctrl+O should still work as a per-session override in either direction.