[FEATURE] Update feature-dev plugin to use opus

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 agents in feature-dev plugin use sonnet. This is a request to update them to use Opus.

Proposed Solution

Update the agents in feature-dev to use opus

Alternative Solutions

_No response_

Priority

High - Significant impact on productivity

Feature Category

Configuration and settings

Use Case Example

_No response_

Additional Context

_No response_