[Docs]: `--builtins` option in setup guide doesn't exist

### Documentation Issue Type

Incorrect information

### Documentation Location

https://cupcake.eqtylab.io/getting-started/usage/claude-code/

### Description

`--builtins` option for `cupcake init` referenced in setup guide doesn't exist.

### Suggested Improvement

_No response_

### Additional Context

_No response_