Update Docs

If you're a Next.js maintainer reviewing PRs, this walks you through keeping docs in sync with code changes. It analyzes git diffs to figure out which documentation files need updates, then guides you step by step through the changes with confirmation prompts before each edit. The useful part is the code-to-docs mapping and the scaffolding templates for new features, plus it handles the AppOnly and PagesOnly component conventions for router-specific content. Includes lint validation to catch formatting issues before you commit. Built for the workflow where you're already looking at a branch and need to methodically work through the documentation debt.