Determine the label-count threshold that should trigger the nudge

## Question

What combined unique node+edge label count should trigger the nudge?

Gather inputs and recommend a starting threshold (10k is a placeholder):
- Any Neptune / graph data-modeling guidance on label cardinality.
- The point at which GE's current schema sync + label-scale UI actually degrade.
- How the pending scaling fixes (#2076, #2077, #2086) move that point.

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> [!IMPORTANT]
> Internal only — this issue is maintained by the core team and is not accepting external contributions.

No files, tests, or entry points are named. Review the Neptune and graph data-modeling guidance, assess where schema sync and the label-scale UI degrade, and account for scaling fixes #2076, #2077, and #2086; done means recommending a starting combined unique node+edge label threshold instead of the 10k placeholder.

Written by the indexing model from the issue text.