Plan mode presents the option to get a rubber-duck review

### Describe the feature or problem you'd like to solve

Make the Rubber Duck review agent a default choice when presented with the Plan mode approval options.

### Proposed solution

Today I use shift+tab to switch to plan mode and create plans. When done the tool asks me to approve them. I want to improve those plans with Rubber duck agent review. So i type 'apply rubber duck review' in as the 4th option to suggest an improvement. This request is to make that option more discoverable as a default choice.

Start by locating the Plan mode approval-options entry point and the existing Rubber Duck review command or label. Check how the approval choices are assembled and verify the Rubber Duck review appears as a default option when a plan is ready for approval.

索引モデルが issue の本文から書いたものです。