Summary

Add a d3-force-based layout transform for network/graph visualizations.

• forceLayout(nodes, links, options) — runs a force simulation synchronously, returns positioned { nodes, links } for use with Dot and Arrow marks
• forceNode(links, options) / forceLink(nodes, options) — curried factory pair following the *Node/*Link convention (like treeNode/treeLink in feat: tree transform #526). Paired factories share a WeakMap-based cache so the simulation runs only once per data array + options reference
• Configurable forces: charge, center, link, collide, x, y, radial — each accepts an options object, a number shorthand, or false to disable. collide, x, y, radial are opt-in (not applied by default)
• setup callback for advanced simulation customization, typed as Simulation<SimulationNodeDatum>

What's included

• Core transform (src/lib/transforms/force.ts) — 432 lines, full TypeScript types and JSDoc
• 20 unit tests (src/lib/transforms/force.test.ts) — both API tiers, custom nodeId, field preservation, invalid link filtering, option shorthands, mutation safety, empty inputs, single-node graph, disconnected graph, cache verification
• 8 examples (src/routes/examples/force/) — basic graph, hover highlighting, link styling, performance-tuned, degree sizing, tooltip, edge weights, bubble chart
• Doc page (src/routes/transforms/force/+page.md) — live example, forceNode/forceLink factory pattern example, full options and forces reference tables
• 16 VR baselines (src/snapshots/force/) — light + dark for all 8 examples
• New dependency: d3-force ^3.0.0 + @types/d3-force ^3.0.10
• Exports added to src/lib/transforms/index.ts
• Sidebar entry in config/sidebar.ts

Design decisions

• Static/synchronous simulation — runs all ticks and returns final positions, matching Observable Plot's approach. A reactive useForceSimulation hook with per-frame animation is planned as a follow-up (would also benefit from canvas Arrow Canvas rendering for Arrow mark #26 and canvas Link Canvas rendering for Link marks #28)
• Curried factory pattern for forceNode/forceLink — same convention as treeNode/treeLink in feat: tree transform #526. Hierarchy transforms produce new record sets rather than modifying existing channel data
• Collision force opt-in — collide defaults to off (like x/y/radial), not on. Graph layouts don't typically need collision detection, and radius=1 has negligible visual effect at typical node sizes
• d3 phyllotaxis initialization — nodes are not pre-positioned at origin; d3-force's built-in phyllotaxis spiral provides better initial spread for convergence
• Removed src/shims.d.ts — 47 lines of unused virtual module type declarations; pnpm check passes with 0 errors without it

Related issues

• Partially addresses Missing transform types #75 (missing transform types)
• Pairs with feat: tree transform #526 (hierarchy transforms) — shares *Node/*Link convention, will have minor merge conflicts in index.ts and sidebar.ts (both append at different positions)
• Future follow-ups: canvas Arrow (Canvas rendering for Arrow mark #26), canvas Link (Canvas rendering for Link marks #28), reactive simulation hook, <Plot canvas> toggle (Option to toggle canvas rendering in entire Plot #32)

Test plan

• pnpm test — 778 tests pass (92 files)
• pnpm lint — 0 errors
• pnpm check — 0 type errors
• pnpm build — successful static build
• VR baselines generated for all 8 examples (light + dark)

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