Add a `writeToFile` helper method

Multiple stages like writing object to files, whether it is JSON schema or a config object.
Add a `writeToFile` utility function such that they are all formatted the same (JSON.stringify args and ending newline)

Look for existing utility functions in the codebase, likely in a utils or helpers directory. The function should accept an object and a file path, use JSON.stringify with consistent formatting (like 2-space indentation), and append a newline. Check how other stages write files to understand the expected pattern. Write a test to verify the output format.

Written by the indexing model from the issue text.