docs(review): clarify Sigma.js role and integration boundaries in listening graph PR

[Copilot]

This update addresses reviewer feedback asking what Sigma is used for in this PR and requests a focused code review of that area. The change is a review/documentation clarification pass (no functional behavior changes), centered on the Sigma integration surface in the frontend.

• Sigma responsibilities (clarified)

  • Sigma is the rendering and interaction runtime for the listening graph UI.
  • Graphology remains the graph data model; Sigma consumes it for WebGL rendering, reducers, and camera control.

• Integration points reviewed

  • GraphView.tsx: SigmaContainer mount, graph loading, layout kickoff, theme/settings.
  • GraphEvents.tsx: event wiring (clickNode, hover) and reducer-driven highlighting/dimming/filter behavior.
  • SearchBar.tsx / PathPanel.tsx: in-memory graph queries via Sigma context and navigation hooks.

• Reviewer-facing notes captured

  • Architecture split is coherent (data model vs renderer vs overlay UI).
  • Follow-up candidates identified in Sigma-adjacent React hooks (dependency completeness / stale-closure risk), without changing runtime behavior in this PR.

<SigmaContainer settings={{ enableEdgeEvents: true }}>
  <GraphLoader data={graphData} />
  <GraphEvents
    onSelectNode={setSelectedNode}
    onHoverNode={setHoveredNode}
    onHoverEdge={setHoveredEdge}
  />
</SigmaContainer>

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