fix: standard lint compliance in pentest.js

- Remove unused requires (http, url)
- Remove unused variables (checkPrototypePollution, timeout, nested→const)
- Fix trailing commas (standard style)
- Fix quotes (single quotes for strings)
- Fix dot notation (res.getHeader('server') not ['server'])
- Fix _body getter (captures mock response body correctly)
- Convert template literals to string concatenation for standard

Author: molty3000