Update Node.js from 20 (EOL) to 24 #161

Summary

.nvmrc and engines pin Node.js 20, which reached end of life in April 2026. wrangler 4.131 (already in devDependencies) requires Node.js 22+, so npm run dev, npm run deploy and wrangler dev fail on the pinned version:

Wrangler requires at least Node.js v22.0.0. You are using v20.20.2.

The CI build still passes because it only runs vite build. The render check job (#160) works around this with node-version: 24.

Proposed Solution

• Move .nvmrc to 24 (Active LTS) and engines.node to >=22.
• Update the Node.js section in the project CLAUDE.md and the README (nvm use 20).
• Let the render check job use .nvmrc again.