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/editor/src/index.tsx

@@ -8,7 +8,11 @@ export {
 // consumed by kind-owned drag actions in @pascal-app/nodes. Stage F
 // cleanup moves these into @pascal-app/nodes (fence/drafting.ts +
 // shared/segment-angle.ts) once every Stage D port is in.
-export { type FencePlanPoint, snapFenceDraftPoint } from './components/tools/fence/fence-drafting'
+export {
+  createFenceOnCurrentLevel,
+  type FencePlanPoint,
+  snapFenceDraftPoint,
+} from './components/tools/fence/fence-drafting'
 export { CursorSphere } from './components/tools/shared/cursor-sphere'
 export {
   formatAngleRadians,
@@ -42,6 +46,9 @@ export type { SaveStatus } from './hooks/use-auto-save'
 // primitive. Public so registry-driven kinds (Phase 5+ Stage D ports)
 // can express their affordances declaratively in their own folder.
 export { type UseDragActionArgs, useDragAction } from './hooks/use-drag-action'
+// Phase 5 Stage D — extras for kind-owned placement tools (FenceTool etc.).
+export { markToolCancelConsumed } from './hooks/use-keyboard'
+export { EDITOR_LAYER } from './lib/constants'
 export type { SceneGraph } from './lib/scene'
 export { applySceneGraphToEditor } from './lib/scene'
 export { triggerSFX } from './lib/sfx-bus'