Add infoview visualization widget for AstroNerve / AstroNet

[Xinze-Li-Moqian]

Context

Layer 0 (AstroNerve + AstroNet) is defined. The development branch has a working widget system (ProofWidgets + d3.js) for the old Hypergraph. Need to bring visualization to Layer 0.

What it should show

• Each nerve as a node (circle/box)
• refs as directed edges between nodes
• Role encoded as edge colour (e.g. input=blue, output=red)
• Nerve id shown on hover
• Record content shown on click/hover

Dependencies

• ProofWidgets (already used on development)
• A JS widget file (d3-based, like widget/atlasGraph.js on development)
• A Lean binding that converts AstroNet → widget props

Acceptance criteria

• #astro.graph myNet renders an interactive graph in the infoview
• Nodes show nerve id, edges show role
• Demo file demonstrates the widget
• Works on both main and development