Phase 5 batch kind: item migrates to registry (always-on)

Item is the first kind to use the `def.renderer` escape hatch (custom
React component with `useGLTF` + drei + interactive widgets) — not
expressible as a pure `def.geometry`. Catalog-backed + multi-host
(free / wall / wall-side / ceiling).

Files added (packages/nodes/src/item/):
 - schema.ts: re-exports ItemNode from core.
 - parametrics.ts: empty groups[]. Item parametrics come from the
   asset's catalog-defined interactive controls (toggles / sliders /
   temperature) — too dynamic for the auto-inspector at Stage A.
   Legacy ItemPanel renders the catalog-driven controls; Phase 5
   Stage E will likely use parametrics.customPanel.
 - definition.ts: capabilities (no `movable` — item move is bespoke
   MoveItemContent that handles attachTo transitions floor↔wall↔
   ceiling mid-drag; capability-driven dispatch keeps legacy mover),
   parametrics, renderer (wrap-export of ItemRenderer), system
   bundling ItemSystem + ItemLightSystem, toolHints matching the
   user's screenshot (Place item / R rotate ccw / T rotate cw /
   Shift free place / Esc cancel). defaults() casts an object
   literal with a stub asset since asset is required by the schema;
   createNode re-parses through ItemNode at runtime.
 - renderer.tsx: wrap-export of legacy ItemRenderer (~280 lines with
   useGLTF + interactive widgets — too much to duplicate at Stage A).
 - system.tsx: bundles ItemSystem + ItemLightSystem.
 - index.ts: barrel.

Files changed:
 - packages/viewer/src/index.ts: new public exports for ItemRenderer,
   ItemSystem, ItemLightSystem.
 - packages/nodes/src/index.ts: appends itemDefinition.
 - packages/editor/src/components/ui/panels/item-panel.tsx: panel
   slider-drag fix recipe applied (nodeRef pattern, drop subscribed
   updateNode dep, drop node from useCallback deps). Item panel has
   scale + position + rotation sliders all subject to the cascade.

Item is the registry's stress test for `def.renderer` escape hatch.
GLB loading via useGLTF + drei works as-is; nothing in the registry
forces a pure-geometry shape on kinds that don't fit.

Phase 5 progress: shelf ✅ spawn ✅ wall ✅ fence ✅ slab ✅ ceiling ✅
door ✅ window ✅ item ✅. Nine kinds on the registry. Stair / roof /
zone / containers remain.

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

packages/nodes/src/item/system.tsx

@@ -0,0 +1,25 @@
+'use client'
+
+import { ItemLightSystem, ItemSystem } from '@pascal-app/viewer'
+
+/**
+ * Registry-driven item system bundle.
+ *
+ *  - **`ItemSystem`** — applies attachTo-driven transforms each frame
+ *    (wall-side z-offset, slab elevation, ceiling mounting).
+ *  - **`ItemLightSystem`** — manages light sources attached to items
+ *    (lamps, ceiling lights, etc.).
+ *
+ * Both are wrapped in `<LegacySystem kind="item">` legacy mounts; with
+ * item registered, those short-circuit and this bundle takes over.
+ */
+const ItemSystems = () => {
+  return (
+    <>
+      <ItemSystem />
+      <ItemLightSystem />
+    </>
+  )
+}
+
+export default ItemSystems