fix(sidebar): enhance node selection to show details for single nodes

[Maystern]

What does this PR do?

Checklist

• Every commit is signed off (git commit -s) — required, CI rejects
  unsigned commits (DCO, see CONTRIBUTING.md)
• Tests pass locally (make -f Makefile.cbm test)
• Lint passes (make -f Makefile.cbm lint-ci)
• New behavior is covered by a test (reproduce-first for bug fixes)

[DeusData]

Thanks for addressing #1197. Two selection cases remain incorrect in this head. nodeIds.size === 1 does not distinguish a leaf from a directory containing one node, so a one-node directory opens details even though Sidebar passes no node for directories. Search results without file_path still pass an empty path and clear selection, while the new GraphNode callback argument is ignored. The patch also duplicates the existing handleNodeClick neighbor and camera behavior. Please route explicit leaf/search-node selection through one canonical node-selection handler and add RED tests for leaf click, one-node directory, search result without file_path, clear selection, and neighbor highlighting.