feat: replace Sigma 2D with Three.js 3D graph renderer

[joel611]

Summary

• Move all layout computation (orbital seed + ForceAtlas2 + noverlap) server-side into Bun — positions baked into `GraphNode` as `x/y/z` before HTML generation
• Replace Sigma.js (2D) + inline vendored FA2/noverlap bundles with vanilla Three.js 3D renderer in the self-contained HTML output
• Depth encoded on z-axis (`depth * -60`), giving the solar system a true 3D funnel shape

Changes

File	What changed
`src/types.ts`	Add `x/y/z` to `GraphNode`
`src/orbital-layout.ts`	Rewrite: arc-per-community seed + `computeLayout()` (FA2 + noverlap via existing graphology deps)
`src/graph-builder.ts`	Call `computeLayout(nodes, edges)` at end of `buildGraph()`
`src/html-report.ts`	Remove ~600 lines of client-side layout/Sigma; add Three.js 3D renderer (InstancedMesh spheres, LineSegments edges, OrbitControls, Raycaster picking, sun glow)
`src/vendor/`	Delete `forceatlas2.bundle.js` + `noverlap.bundle.js`; add `three.bundle.js` (Three.js + OrbitControls)

Net effect

• -1568 lines removed (Sigma, inline FA2/noverlap, duplicate layout function)
• 96 tests pass (2 new z-depth encoding tests added)

Test plan

• `bun test` — 96 pass
• `bun run src/index.ts ` — generates HTML, open and verify 3D solar system renders
• OrbitControls: rotate, zoom, pan work
• Hover tooltip appears on node mouseover
• Click node opens detail panel
• Sidebar filters hide/show nodes correctly
• Stats and Links tabs still work

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