chore: upgrade Node.js to 24

[rahulkanneri-2u]

Description

Upgrade course-discovery to use Node.js 24 for frontend asset builds.

This adds a repository-level Node version declaration and a dedicated CI job to validate the production frontend asset build on Node 24.

Changes

• Add .nvmrc with Node.js 24.
• Add a frontend_assets CI job that:
  • uses the Node version defined in .nvmrc;
  • installs locked production JavaScript dependencies;
  • installs Bower dependencies;
  • runs the webpack asset build.

The build retains NODE_OPTIONS=--openssl-legacy-provider, matching the current public-dockerfiles Node 24 build configuration. This is needed for the existing legacy loader/MD4 hashing behavior and should be removed in a future dependency-modernization follow-up.

Testing

Validated locally with Node.js 24:

npm ci --omit=dev
bower install --allow-root --production
NODE_OPTIONS=--openssl-legacy-provider webpack --config webpack.config.js --progress