ci: fix next build failure and update workflow actions

[katsugtgz]

Fixes the failing deploy workflow and updates the workflow actions to current majors.

The deploy job has failed on every run since Aug 8. The build step dies because a stray npm install @vercel/speed-insights line was pasted at the end of app/layout.tsx, after the closing brace, which is a syntax error webpack rejects. The package is already in package.json, so the line is simply removed.

There is a second failure hiding behind the first: next build sees app/layout.tsx, finds no TypeScript toolchain, and auto-installs devDependencies mid-build. That currently resolves to typescript 7, which crashes the Next.js 14 build worker with The "id" argument must be of type string. Pinning typescript 5 as a devDependency and committing the generated tsconfig.json and next-env.d.ts makes the build deterministic.

Also updates the GitHub Actions references that were on deprecated node16/node20 runtimes or old majors: actions/checkout v2/v3/v4 to v7, actions/setup-node v3/v4 to v7, github/codeql-action v3 to v4, actions/configure-pages v5 to v6, actions/upload-pages-artifact v3 to v5, actions/deploy-pages v4 to v5. actions/jekyll-build-pages stays on v1, still the current major. The node-version pins 16 and 18 are EOL and move to 20 LTS.

Validation:

• npm ci then npx next build on this branch: compiles and prerenders successfully
• all six workflow files pass YAML parse
• latest majors resolved live from each action's releases endpoint (checkout v7.0.1, setup-node v7.0.0, codeql-action v4.37.9, configure-pages v6.0.0, upload-pages-artifact v5.0.0, deploy-pages v5.0.1)

Scope: .github/workflows/*, app/layout.tsx, package.json, package-lock.json, tsconfig.json, next-env.d.ts.

Note: workflow runs on this PR are queued behind maintainer approval (action_required), the usual state for a first PR from a fork. The validation above was run locally on the branch head.