Add a complete new learning module covering the Node.js ecosystem with
10 sections and 8 interactive SVG visualizations.

Sections:
- Introduction — overview, stats, company examples, learning journey
- Event Loop — 5-phase architecture, microtasks, libuv thread pool
- Async Programming — callbacks, promises, async/await evolution
- Buffers & Streams — Buffer API, 4 stream types, backpressure
- Scaling — Cluster vs Worker Threads, PM2, comparison table
- Memory Management — V8 heap, Minor/Major GC, memory leak patterns
- Module System — CommonJS vs ESM syntax, tree-shaking, live bindings
- Package Managers — npm vs Yarn vs pnpm architecture and trade-offs
- Frameworks — Express, Fastify, NestJS, Koa, Hono comparison
- Runtime Wars — Node.js vs Deno vs Bun benchmarks and decision guide

Visualizations:
- EventLoopViz — animated 5-phase loop with microtask queue
- StreamsBuffersViz — streaming pipeline with backpressure demo
- ClusterVsWorkerViz — tabbed cluster vs worker threads comparison
- V8MemoryViz — interactive V8 heap with GC trigger controls
- PackageManagerViz — npm/yarn/pnpm install simulation
- ModuleSystemViz — CJS vs ESM step-through loading
- RuntimeComparisonViz — Node vs Deno vs Bun architecture comparison
- FrameworksViz — Express/Fastify/NestJS/Koa/Hono performance bars

Integration:
- Add 'nodejs' color scheme (green/emerald/lime) to theme.ts
- Add lazy-loaded /nodejs route in App.tsx
- Add Node.js to Header navigation (Frameworks group)
- Add 10 sidebar entries + getSectionFromPath + green color in Sidebar.tsx
- Add Node.js module card to Home page
- Update stats to 12+ modules, 78+ visualizations
- Update README with Node.js Ecosystem module info