Next.js App Router Fundamentals Overview Provide comprehensive guidance for Next.js App Router (Next.js 13+), covering migration from Pages Router, file-based routing conventions, layouts, metadata handling, and modern Next.js patterns. TypeScript: NEVER Use Type CRITICAL RULE: This codebase has enabled. Using will cause build failures. ❌ WRONG: ✅ CORRECT: Common Next.js Type Patterns When to Use This Skill Use this skill when: - Migrating from Pages Router ( directory) to App Router ( directory) - Creating Next.js 13+ applications from scratch - Working with layouts, templates, and nested ro…