fix: create parent directories for export destinations

[rogerchappel]

Summary

• add a CLI regression test for nested --out destinations and exported content
• create missing parent directories before writing an export file
• document stdout and file destination behavior

Commits

• 5d3bf48 test: cover nested export destinations
• dc8785b fix: create parent directories for exports
• ff45319 docs: describe export destination behavior

Verification

• npm run release:check
• git diff --check

All checks pass locally.