When phpcs.xml sets installed_paths to a relative path (e.g.
vendor/slevomat/coding-standard), running phpcs from the file's
directory causes it to fail because the path is resolved relative to
cwd rather than the config file location.
Change cwd to find the nearest composer.json and use that directory,
matching how most PHP ecosystem tools expect to operate.
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
