Phase 5 Stage E: full kind migration into packages/nodes

Wholesale move of every remaining kind into its own subdirectory under
`packages/nodes/src/`, finishing the registry-driven migration. Each
kind now ships its definition, schema (re-exported from core), and any
of `geometry` / `renderer` / `system` / `floorplan` / `tool` /
`move-tool` / `panel` / `floorplan-move` / `floorplan-affordances` /
`parametrics` / `preview` it needs — no per-kind code remains under
`packages/editor/src/components/tools/` or
`packages/viewer/src/components/renderers/`.

Deleted (replaced by registry-driven equivalents):
- `tools/{ceiling,column,door,fence,item,slab,spawn,wall,window}/...`
  (boundary editors, hole editors, placement tools, move tools,
  endpoint movers, curve tools, helpers, math libs)
- `ui/helpers/{ceiling,slab,wall}-helper.tsx`
- `ui/panels/{column,door,elevator,item,roof,roof-segment,spawn,
  stair,stair-segment,wall,window}-panel.tsx`
- `viewer/src/components/renderers/{building,ceiling,column,door,
  elevator,fence,guide,item,level,roof,roof-segment,scan,site,slab,
  spawn,stair,stair-segment,wall,window,zone}-renderer.tsx`
- `viewer/src/components/viewer/legacy-system.tsx`

Added under `packages/nodes/src/`:
- `building/`, `column/`, `elevator/`, `guide/`, `level/`, `roof/`,
  `roof-segment/`, `scan/`, `shared/`, `site/`, `stair/`,
  `stair-segment/` packages with definition + schema + renderer / system
  / floorplan / panel as appropriate.
- New `floorplan-move.ts` for every kind that supports 2D moves
  (ceiling, door, item, shelf, slab, window) — single registry-driven
  dispatch path via `def.floorplanMoveTarget`.
- New `floorplan-affordances.ts` for kinds with polygon / endpoint
  drags (ceiling, fence, slab, wall) — using the shared
  `polygon-vertex-affordance` factories.
- New per-kind `panel.tsx` for kinds with custom inspector content
  (door, item, shelf, spawn, wall, window).
- New per-kind `tool.tsx` for placement (door, item, shelf, window).
- New per-kind `move-tool.tsx` for kinds with custom 3D move flows
  (door, item, slab, window).

Coordinator + manager updates in `packages/editor/`:
- `tool-manager.tsx` resolves tools from the registry only — no
  hardcoded type→component map.
- `panel-manager.tsx` resolves inspector panels the same way.
- `placement-{coordinator,strategies,types}.ts` extended with
  shelf-surface placement.
- `selection-manager.tsx` adds the registry-selectable fallback.
- `floorplan-panel.tsx`, `floorplan-background-placement.ts`,
  `floorplan-render-context.tsx` updated for the registry layer's new
  contract (props, affordance dispatch, render context).

Viewer updates:
- `viewer/index.tsx` drops legacy renderer mounts.
- `node-renderer.tsx` resolves by registry only.
- `scene-bvh.tsx`, `use-node-events.ts`, `level-system.tsx`,
  `wall-cutout.tsx`, `zone-system.tsx`, `materials.ts` adjusted for
  the registry-only world.

Sidebar tree nodes for ceiling / fence / slab / shelf / tree-node
updated to read from the registered nodes instead of the deleted
legacy renderer trees.

Wiki: new `plugin-authoring.md` page, README index updated.

Tests in `packages/nodes/src/index.test.ts` validate every registered
kind has the required shape.

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

packages/nodes/src/slab/move-tool.tsx

@@ -64,6 +64,29 @@ function setMeshOffset(id: AnyNodeId, deltaX: number, deltaZ: number): void {
   if (mesh) mesh.position.set(deltaX, 0, deltaZ)
 }
 
+/**
+ * Distinguish 3D-canvas grid events (which this tool handles) from
+ * 2D floor-plan grid events (which `slabFloorplanMoveTarget` +
+ * `FloorplanRegistryMoveOverlay` Path 1 handle). The 2D scene wraps
+ * everything in `[data-floorplan-scene]`; if the native event's target
+ * is inside that subtree, the event belongs to the 2D mover. Without
+ * this guard, both paths would write the polygon on commit and produce
+ * two history entries / a double-translation.
+ */
+function isFloorplanSourcedEvent(event: GridEvent): boolean {
+  // ThreeEvent (3D) wraps the DOM PointerEvent under `.nativeEvent`;
+  // the 2D emitter passes the raw PointerEvent directly. Cover both.
+  const native: unknown = event.nativeEvent
+  const candidate =
+    (native as { target?: unknown; nativeEvent?: { target?: unknown } } | null) ?? null
+  const target =
+    (candidate?.target as Element | null | undefined) ??
+    (candidate?.nativeEvent as { target?: Element | null } | undefined)?.target ??
+    null
+  if (!target || typeof (target as Element).closest !== 'function') return false
+  return (target as Element).closest('[data-floorplan-scene]') != null
+}
+
 export const MoveSlabTool: React.FC<{ node: SlabNode }> = ({ node }) => {
   const activatedAtRef = useRef<number>(Date.now())
   const originalPolygonRef = useRef(node.polygon.map(([x, z]) => [x, z] as [number, number]))
@@ -129,6 +152,7 @@ export const MoveSlabTool: React.FC<{ node: SlabNode }> = ({ node }) => {
     }
 
     const onGridMove = (event: GridEvent) => {
+      if (isFloorplanSourcedEvent(event)) return
       const [localX, localZ] = snapFenceDraftPoint({
         point: [event.localPosition[0], event.localPosition[2]],
         walls: levelWalls,
@@ -150,6 +174,7 @@ export const MoveSlabTool: React.FC<{ node: SlabNode }> = ({ node }) => {
     }
 
     const onGridClick = (event: GridEvent) => {
+      if (isFloorplanSourcedEvent(event)) return
       if (Date.now() - activatedAtRef.current < 150) {
         event.nativeEvent?.stopPropagation?.()
         return