[Feature Request] Allow expansion of RDF classes

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**Graph Explorer Version (and Graph Database and Version used if applicable)**
Any

**Is your feature request related to a problem? Please describe.**
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None

**Describe the solution you'd like**
A clear and concise description of what you want to happen.
Current solution allows user to expand individuals but not classes. Feature request is to allow user to expand a class. For example if :Mike is an instance of class :Person, I can fully expand :Mike, but I cannot expand :Person to look at its neighbors. Some of those neighbors could be interesting to follow in the canvas. For example, if :Person is linked to a SHACL shape or an R2RML mapping, I might want to inspect the shape or mapping.

**Additional context**
Add any other context or screenshots about the feature request here. Describe any alternatives you've considered.

Start by locating the existing individual-expansion flow in the TypeScript/React Graph Explorer UI and its RDF handling. Compare current class and individual behavior, then define the interaction and validation needed to expand RDF classes and inspect neighboring nodes; done means class expansion works in the canvas without regressing individual expansion.

Written by the indexing model from the issue text.