chore: upgrade Node.js to latest LTS (24) across the repo

[josephfusco]

Context

Node.js 20 entered EOL in April 2026, and Node.js 18 has been EOL since April 2025. Node.js 24 became the active LTS in October 2025 and is the current latest LTS. Node.js 22 remains in active LTS until April 2027.

We should align the repository to the supported Node.js release line:

• Default Node version everywhere we currently pin to 22 should be bumped to 24.
• Anywhere we still default to 20 or 18 should be bumped to 24.
• CI test matrices should drop 18 and 20 entirely (both EOL) and become ['22', '24'].
• engines.node in every package.json (root + workspaces) should be raised to >=22.
• Any existing .nvmrc / .node-version file should be set to 24 (we won't create new ones).

Scope

• .github/workflows/*.yml
• .github/actions/cache-restore/action.yml
• .nvmrc
• package.json engines.node (root + packages/*, examples/next/*)

No Docker base image changes are needed; the only Docker images in this repo are WordPress/PHP, not Node.

Coordination

PR #2368 is currently bumping actions/* v4 -> v5 across the same workflow files. The two changesets touch different lines (action version vs node-version), so they should merge cleanly, but reviewers should be aware of the overlap.

Follow-up

A PR implementing this will be linked here.

[josephfusco]

Splitting this into two phases.

Phase 1 — CI matrix only (#2371, open now)

• Drops Node 18 from CI (EOL since March 2025)
• Keeps Node 20 in the matrix (our customers still deploy on it)
• Adds Node 24 (new Active LTS as of October 2025)
• Updates .nvmrc 18 → 22 and the bundle-analysis pin 20 → 22
• No package.json engines change. No customer impact.

Phase 2 — Engines bump + major release (deferred, no schedule)

• Bump engines.node to >=22 across all published @faustwp/* packages
• Release as a major version (4.0.0 for core/cli, matching the v3.0.0 precedent that dropped Node 16)
• Migration doc at docs/how-to/upgrade-node-runtime/index.md
• Changeset announcement; possibly Discord/blog
• Triggered when customer adoption of Node 22+ has organically moved far enough that this isn't a forced runtime upgrade for active deployments

This issue stays open to track Phase 2.