Integrate code review extension in PR workflow #468

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
• Clean up tasks(e.g. SetupGithubCommands, generate_examples.sh, gemini-review prompts) filed separately in Cleanup gemini-review related docs/text after code review extension integration #478