feat(viewer): enhance node inspector

[forhappy]

Summary

• show incoming and outgoing node counts in selected-node metadata
• group directed relationships by neighboring node while preserving relation types and multiplicity
• add icon-led Callers, Callees, Impact, source, and community actions
• keep the inspector accessible and responsive down to its 280px minimum width
• regenerate the bundled viewer assets

Compatibility

Presentation-only viewer change. No graph schema or public contract changes.

Testing

• npm run typecheck:js
• npm run test:js (230 viewer tests, 143 VS Code tests, 88 browser tests)
• node scripts/check_viewer_assets.mjs
• git diff --check