Allow disabling Rubber Duck for a session

### Problem

I want the option to turn off Rubber Duck for an individual session. In some sessions I want to conserve tokens or move faster without an additional critique pass.

I can ask for this behavior in the prompt, but that is less discoverable and reliable than a dedicated control.

### Requested behavior

Add a per-session toggle or similar setting that disables Rubber Duck for that session. The setting should be easy to change without requiring custom prompt instructions.

### Use cases

- Reduce token usage when an additional review pass is not needed.
- Get to implementation faster for straightforward or time-sensitive work.
- Choose when the extra critique step is valuable on a session-by-session basis.

该 issue 未指定任何文件或测试；首先定位桌面应用中的会话控制项和 Rubber Duck 流程。确定可以在哪里提供按会话设置，然后验证更改该设置只会影响当前会话并跳过额外的批评环节，同时保持其他会话不变。

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