chore: prepare release v0.2.0

refactor(extension): rename AI Code Review to CodeSage

- Rename extension from "AI Code Review" to "CodeSage"
- Update README.md with new extension name and description
- Modify package.json and package-lock.json to reflect new name
- Update source code files to use new command prefixes and configuration settings
- Refactor some code to improve readability and maintainability