Integrate code review extension in PR workflow

[cynthialong0-0]

Problem

Code review agent mcp server (mentioned in #236) does not have near future plan for implementation, the alternative is to install the code review extension instead to do reviews.

Tasks

• Update code review extension to leave comments in PR request and locally configured by args/settings
• Update the PR workflow to use extension and remove the custom PR review prompt

[gemini-cli]

🤖 Hi @cynthialong0-0, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.