First Stage D port — `CurveFenceTool` (178 LoC legacy) split into a pure
`DragAction` primitive (`packages/nodes/src/fence/actions/curve.ts`) plus
a thin React wrapper (`packages/nodes/src/fence/curve-tool.tsx`) that
feeds it through `useDragAction`. The kind declares the affordance via
`def.affordanceTools.curve`; ToolManager lazy-loads it at runtime when
`useEditor.curvingFence` activates. Falls back to the legacy
`CurveFenceTool` for any kind that hasn't been ported.
The lazy-load dispatch dodges the editor→nodes circular dep (nodes
already depends on editor for `useDragAction` + `CursorSphere`).
Establishes the pattern for the remaining fence affordances
(`MoveFenceEndpoint`, `MoveFence`, placement) and for slab/ceiling/wall
D ports.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
