Summary

• When a tag is selected, the local 3D graph shows an ego co-tag cloud instead of the empty "Select a concept" state.
• Center node is the selected tag; neighbors are tags that co-occur on the same concepts.
• Node size and link opacity/layout use Jaccard togetherness (with a co-count boost); neighborhood capped at 40.
• Clicking a co-tag navigates to that tag and rebuilds the ego graph around it.

Test plan

• okf view a bundle with multi-tag concepts (e.g. samples/the-law)
• Select a tag from a concept's tags or the Tags panel; confirm local graph shows co-tags
• Confirm note shows co-tag/link counts (or "No co-occurring tags" for isolates)
• Click a neighbor tag; selection and graph update
• Select a concept again; local graph returns to concept neighborhood
• dotnet test --filter FullyQualifiedName~BundleViewer