Add Janus Studio to the Visualization section

**Describe the feature:**

Add Janus Studio (https://github.com/Zorabi/janus-studio) to the root README “Visualization” section.

Janus Studio is an open-source, cross-platform desktop IDE for JanusGraph and Apache TinkerPop. It includes interactive graph visualization, a Gremlin workbench, Schema management, and ConfiguredGraphFactory support.

Suggested entry:

* [Janus Studio](https://github.com/Zorabi/janus-studio) - a cross-platform desktop IDE for JanusGraph and Apache TinkerPop with interactive graph visualization.

**Describe a specific use case for the feature:**

This helps users looking through the JanusGraph visualization ecosystem discover a desktop-based, open-source option for querying, managing, and visualizing JanusGraph databases.

Edit the root README and locate the Visualization section. Add the suggested Janus Studio link and description, then verify that the entry appears in the correct section with the requested URL and wording.

Written by the indexing model from the issue text.