[codex] Add Node 24 compatibility CI

[mashbean]

Summary

Adds a Node 24 compatibility lane to the existing reusable build workflow while keeping the default runtime on Node 18.

Changes:

• widens engines.node to allow Node 18 and Node 24
• adds a node_version input to .github/workflows/build.yml, defaulting to 18
• runs the PR test workflow with a Node 18 and Node 24 matrix
• updates the workflow checkout action to actions/checkout@v4
• refreshes lockfile metadata with npm 11 so npm ci can run under Node 24

Why

This is the compatibility PR only. Deploy workflows that do not pass node_version still use the default Node 18 path, and the Dockerfile remains on node:18-alpine. That preserves the current production rollback line while allowing CI to prove Node 24 compatibility.

Validation

• npx -p node@24 -p npm@11 npm ci, passed with an existing @matters/matters-editor@0.3.0-alpha.4 engine warning
• npx -y node@24 -e "import('bcrypt').then(...)", confirmed bcrypt loads
• npx -y node@24 node_modules/typescript/bin/tsc -p ., passed
• npx -p node@24 -p npm@11 npm run lint, passed
• npx -p node@18 -p npm@10 npm ci --ignore-scripts, passed as lockfile rollback-line check

Full test execution is left to GitHub Actions because the workflow provides Redis, Postgres, and stripe-mock services.

Known follow-up

@matters/matters-editor@0.3.0-alpha.4 declares node >=18.19 <19.0, so npm emits an engine warning under Node 24. It is not a hard install failure. The shared-package follow-up should publish or consume a Node 24-compatible editor package before production runtime cutover.

Rollback

Revert this PR, or leave it merged and omit node_version from deployment workflow calls. The reusable workflow defaults to Node 18, and the Dockerfile still uses Node 18.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.68%. Comparing base (086cd37) to head (c1ac158).
⚠️ Report is 7 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4847      +/-   ##
===========================================
+ Coverage    72.57%   72.68%   +0.10%     
===========================================
  Files         1067     1067              
  Lines        21164    21259      +95     
  Branches      4619     4691      +72     
===========================================
+ Hits         15360    15452      +92     
- Misses        5327     5328       +1     
- Partials       477      479       +2     

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