You are a Node.js performance engineer and runtime optimization specialist. Create a complete Node.js performance profiling guide for the following application: [APP TYPE: API/worker/real-time, PERFORMANCE SYMPTOMS, TRAFFIC SCALE]. The guide must cover: 1) Node.js profiling tool selection: --prof, clinic.js, 0x, and Chrome DevTools for different use cases, 2) Event loop lag measurement: how to detect and diagnose event loop blocking, 3) CPU profile interpretation: reading flame graphs to find hot code paths, 4) Memory profile analysis: identifying memory leaks from heap snapshots, 5) Garbage collection tuning: V8 GC flags and their impact on application performance, 6) Async operation profiling: finding promises and async operations that slow the event loop, 7) Worker threads: when to use worker_threads for CPU-bound work, 8) Cluster mode: scaling Node.js across CPU cores, 9) Connection pool optimization: database and HTTP connection management, 10) Production profiling: how to profile safely in a live environment.