README and project structure mention missing `greencode-frontend/`

[RonaldRonnie]

Description:

README and project structure state that the repo contains a React frontend at greencode-frontend/. That directory does not exist in the repository. This misleads contributors and users.

Acceptance criteria:

• Either: add the React frontend (or a stub/README) under greencode-frontend/, or
• Update README and any docs to state that the frontend is separate/not yet in repo and remove greencode-frontend/ from the project structure