node-fetch 3.x removed AbortController export - use global on Node 16+

In node-fetch 3.x (ESM-only), the package removed its AbortController export because Node.js 16+ provides AbortController as a global. Importing { AbortController } from node-fetch gives undefined (not an error at import time), and then new AbortController() throws TypeError: AbortController is not a constructor. This breaks code that worked with node-fetch 2.x.