check prettier formatting in validate script

Without this, formatting is not checked in CI and only applied if the precommit hooks are installed, which is optional

Options:
- Add `prettier --list-different` to validate command
- Integrate prettier rules into ESLint (probably preferred for JS)

Start by locating the validate command and reviewing how the optional precommit hooks currently apply formatting. Compare the two proposed approaches—adding prettier --list-different or integrating prettier rules into ESLint—and confirm that CI detects formatting differences without requiring hooks.

Written by the indexing model from the issue text.