Add baked-in Node.js server template (successor to nodejs-template)

## Context

We are archiving the standalone [nodejs-template](https://github.com/asyncapi/nodejs-template) repo. Users still need a maintained way to generate Node.js servers from AsyncAPI documents inside the generator monorepo.

The legacy [nodejs-ws-template](https://github.com/asyncapi/nodejs-ws-template) can serve as a reference for WebSocket-specific patterns, but the goal here is a **new baked-in template** aligned with current generator architecture (`packages/templates`, React SDK, `@asyncapi/keeper`, shared components/helpers).

## Goal

Add a baked-in Node.js server template to `@asyncapi/generator` that replaces the archived standalone template — multi-protocol where feasible, runtime message validation, and integration/acceptance tests following existing baked-in template conventions.

## References

- https://github.com/asyncapi/nodejs-template (to archive)
- https://github.com/asyncapi/nodejs-ws-template
- [Baked-in templates guide](https://github.com/asyncapi/generator/blob/master/apps/generator/docs/baked-in-templates.md)

Start with the baked-in templates guide at apps/generator/docs/baked-in-templates.md and inspect packages/templates, along with the archived nodejs-template and nodejs-ws-template references. Follow the current React SDK, @asyncapi/keeper, and shared components/helpers conventions. Done means a maintained baked-in Node.js server template with feasible multi-protocol support, runtime message validation, and integration/acceptance tests.

Written by the indexing model from the issue text.