feat: add support for RabbitMQ message broker node

[NureniJamiu]

Is your feature request related to a problem? Please describe.

Users currently have access to computing nodes (Ubuntu, ASG) and database/cache nodes (Postgres, Mongo, Redis). But, there is no message broker node. This makes it impossible to design or simulate asynchronous architectures, message queues, and pub-sub systems visually on the canvas.

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Describe the solution you'd like

I would like to add a new RabbitMQ message broker node type, which will back onto the official rabbitmq:3-management Docker image.

Key details of the implementation:

1. I'll introduce a standard 'rabbitmq' node type in ContainerManager which will pull the rabbitmq:3-management image on container startup.
2. I'll map container port 15672 (HTTP management UI) to a dynamic public port on the host machine.
3. I'll add a customized RabbitMQ inspect modal which will displau the active container status, default login credentials (guest / guest), and a direct link to open the Management Console in the browser. It should also include a cheat sheet of common exchanges/queues patterns and commands.
4. Then I'll finally register the node under a new "Message Brokers" category inside the Node Library (using an appropriate icon from lucide-react).

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Describe alternatives you've considered

• Memcached / ActiveMQ / Kafka: RabbitMQ is preferred as the initial broker because it is lightweight, extremely common in system design interviews, and comes with a beautiful, pre-installed web administration dashboard (rabbitmq:3-management) that runs perfectly in local-first Docker environments.

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Additional context

This starts the implementation of the Message Brokers roadmap item listed under "Coming Very Soon" in the project README.