chore: migrate from Node 18 to Node 20

[devin-ai-integration]

Summary

Migrates the TODO List application runtime from Node.js 18 to Node.js 20 (one major version increment per the migration playbook).

Migration Checklist

Area	Change
.nvmrc	18 → 20
package.json engines	>=18.0.0 <19.0.0 → >=20.0.0 <21.0.0
package.json description	Updated to reference Node.js 20
.eslintrc.json	es2021 / ecmaVersion 2021 → es2022 / ecmaVersion 2022
better-sqlite3	Native addon rebuilt for Node 20 (v9.6.0 compatible, no version bump needed)

What was NOT changed (and why)

• Express stays at 4.x — runtime and framework upgrades are independent for Node.js; Express 5 migration can be done separately.
• ESLint stays at 8.x — ESLint 9 requires migrating to flat config (eslint.config.js), which is a separate effort.
• No deprecated API usage found — scanned for url.parse(), Buffer() constructor, fs.exists(), require('punycode'), process.binding(), util.isArray(), util.isFunction(). None present.
• No Dockerfile or CI workflow files — no additional version references to update.

Verification

• 54/54 tests pass on Node 20.20.2 (same as baseline on Node 18)
• Lint clean (eslint src/ tests/)
• 0 npm audit vulnerabilities
• better-sqlite3 native addon rebuilt and verified functional

Review & Testing Checklist for Human

• Run nvm use 20 && npm rebuild && npm test to verify all 54 tests pass on your machine
• Run npm start and verify the app serves at http://localhost:3000
• Verify better-sqlite3 WAL mode and CRUD operations work via the UI or API

Notes

• Node 20 is an LTS release (Active LTS until Oct 2024, Maintenance until Apr 2026). Consider planning the Node 22 migration as a follow-up.
• The better-sqlite3 native addon (v9.6.0) supports Node 20 out of the box — only a rebuild is needed, no version bump required.

Link to Devin session: https://app.devin.ai/sessions/b85d4eb55ec54bba8869439b7055afbd
Requested by: @clivingston-cognition

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✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

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