[INSTALL-4] Bare-metal prerequisite checklist and convenience script missing

## Problem

The bare-metal installation guide does not list required system prerequisites. On a fresh machine, users encounter `cmake` and `ninja-build` not installed, NCCL missing, and no guidance on setting `CUDA_HOME` or `CPATH`. Each failure requires manual debugging and is not mentioned in the docs.

## Suggested fix

- Publish a complete prerequisite checklist covering: `cmake`, `ninja-build`, NCCL, and required environment variables (`CUDA_HOME`, `CPATH`).
- Provide a convenience bash script that installs all prerequisites and runs the full bare-metal setup.