Kiro: Duplicate "Generate Commit Message" entries in Source Control sparkle button dropdown

## Problem

In the Source Control view, the "Generate Commit Message" sparkle button (✨) shows a dropdown with two identical "Generate Commit Message" entries.

## Steps to reproduce the issue

1. Open a workspace with Git changes in Kiro
2. Go to the Source Control view
3. Click the sparkle (✨) button next to the commit message input field
4. Observe two identical "Generate Commit Message" options in the dropdown

## Expected behavior

Only a single "Generate Commit Message" option should appear in the dropdown menu.

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Windows
- Kiro version: 0.11.130

Start in the Source Control view by tracing the sparkle button next to the commit message input and the dropdown entries it creates. Reproduce the issue in Kiro with Git changes, then identify why two identical Generate Commit Message options are registered or rendered. Done means the dropdown contains exactly one entry and the existing generation action still works.

Written by the indexing model from the issue text.