ci: migrate Node workflow to reusable npm build

[vitormattos]

Summary

Migrate the deprecated .github/workflows/node.yml copy to the supported LibreCode npm-build.yml caller.

Nextcloud's current node.yml is intentionally a failing migration stub and is scheduled for removal at the end of 2026. LibreCode now follows the successor model instead of carrying the obsolete filename.

The reusable implementation is pinned to d96f4b5dcf780dea20d8843f54c4b52207dc25fd and:

• uses public GitHub-hosted runners;
• uses checkout v7 and setup-node v7;
• honors the project's Node engine;
• avoids globally installing a PR-controlled npm range;
• validates package-lock metadata with a pinned helper;
• keeps the final job/check name node for compatibility with existing branch protection conventions.

This PR intentionally renames the workflow file rather than preserving the deprecated upstream filename.