Add LLMGraph

[abahocodes]

Add LLMGraph to the AI Platforms section.

Why is this awesome?

• No-code visual builder for LLM/AI workflows — build without writing code.
• Turns your docs and models into RAG chatbots and AI agents.
• Deploys each workflow to a REST API and an embeddable chat widget in one click.

Added as a single entry in the AI Platforms section (after Dify), matching the list's [Name](link) - Description. format.

[abahocodes]

Thanks for maintaining awesome-nocode-lowcode. This PR adds LLMGraph, a no-code visual builder for LLM workflows that deploy to a REST API and chat widget. A review whenever you have a moment would be appreciated, and I can adjust the entry.