Phase 5 Stage D fence: port FenceTool placement to def.tool

Fourth and final Stage D fence affordance — the placement tool itself.

Unlike the drag affordances (curve / move / endpoint), placement is a
two-click flow with state across grid events, not a single drag-down →
drag-up lifecycle. `DragAction` doesn't fit; the component owns its
own emitter subscriptions directly. The kind exposes it via
`def.tool: () => import('./tool')` and ToolManager's existing
`getRegistryTool()` lookup mounts it (legacy `tools.structure.fence =
FenceTool` falls through when the registry entry is missing).

Adds transitional exports from `@pascal-app/editor` for the helpers
the kind-owned tool needs at module scope: `createFenceOnCurrentLevel`,
`markToolCancelConsumed`, `EDITOR_LAYER`. Stage F cleanup moves these
into `@pascal-app/nodes` once every consumer is registry-driven.

Fence Stage D is now complete. Per-kind progress: A ✅ B ✅ C ✅ D ✅
(four affordances ported — curve, move-endpoint, move, placement).
E (drop legacy panel) and F (cleanup) pending across all kinds.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/nodes/src/fence/definition.ts

@@ -58,6 +58,13 @@ export const fenceDefinition: NodeDefinition<typeof FenceNode> = {
 
   parametrics: fenceParametrics,
 
+  // Stage D: kind-owned placement tool. Two-click flow (start → end)
+  // with live preview, length / angle HUD, snap to walls / fences /
+  // grid. Mounted by ToolManager when `useEditor.tool === 'fence'`
+  // via the registry's getRegistryTool() — falls back to the legacy
+  // tools[phase][tool] map when missing.
+  tool: () => import('./tool'),
+
   // Stage B: pure geometry function. Generic <GeometrySystem> rebuilds
   // on dirtyNodes; <ParametricNodeRenderer> mounts the empty group.
   // `renderer` + `system` fields dropped along with their files.