[FEATURE] Add toggle thinking mode into the chat UI

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The CLI have them, it makes no sense if the interactive UI doesn't have it.

Proposed Solution

Add the thinking toggle for interactive UI.

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

Configuration and settings

Use Case Example

_No response_

Additional Context

_No response_