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

Structurally identical to slab. Stage A migration: registers the kind,
wraps the legacy renderer + system, applies the panel slider-drag fix
recipe.

Files added (packages/nodes/src/ceiling/):
 - schema.ts: re-exports CeilingNode from core.
 - parametrics.ts: height slider only. Polygon + holes via floor-plan
   editors.
 - definition.ts: capabilities (no `movable`, `surfaces.top` mapped to
   `height`), relations (hosts: ['item'] for ceiling-mounted lights /
   fans, cascadeDelete: 'descendants'), toolHints, parametrics.
 - renderer.tsx: wrap-export of legacy CeilingRenderer. The legacy
   renderer uses TSL shader code for grid-line patterns (~100 lines);
   not worth duplicating at Stage A. Per-stage migration plan in
   plans/editor-node-registry.md moves the renderer body into this
   folder at Stage B/F.
 - system.tsx: re-exports legacy CeilingSystem.
 - index.ts: barrel.

Files changed:
 - packages/viewer/src/index.ts: new public exports for CeilingRenderer
   + CeilingSystem.
 - packages/nodes/src/index.ts: appends ceilingDefinition.
 - packages/editor/src/components/ui/panels/ceiling-panel.tsx: panel
   slider-drag fix recipe applied (nodeRef pattern, useScene.getState()
   inside handler, drop subscribed updateNode dep) so the height
   slider doesn't trigger the same cascade fence + wall + slab fixed.

Phase 5 progress: shelf ✅, spawn ✅, wall ✅, fence ✅, slab ✅, ceiling ✅.
Six kinds on the registry. Door / window / item / stair / roof / zone
follow.

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

packages/nodes/src/ceiling/definition.ts

@@ -0,0 +1,80 @@
+import type { NodeDefinition } from '@pascal-app/core'
+import { ceilingParametrics } from './parametrics'
+import { CeilingNode } from './schema'
+
+/**
+ * Ceiling — Phase 5 batch kind, polygon-based. Structurally identical
+ * to slab but mounted at `height` rather than `elevation`.
+ *
+ * Capabilities:
+ *  - **No `movable`**: ceiling move is bespoke via legacy `MoveCeilingTool`
+ *    + the floor-plan boundary / hole editors. Capability-driven dispatch
+ *    keeps the legacy mover (preserves polygon-aware behavior).
+ *  - **`surfaces.top`**: items host on the ceiling at `height`.
+ *  - `selectable`, `duplicable`, `deletable` standard.
+ *
+ * Relations: `hosts: ['item']` for ceiling-mounted items (lights, fans).
+ * `cascadeDelete: 'descendants'` removes hosted items on ceiling delete.
+ */
+export const ceilingDefinition: NodeDefinition<typeof CeilingNode> = {
+  kind: 'ceiling',
+  schemaVersion: 1,
+  schema: CeilingNode,
+  category: 'structure',
+
+  defaults: () => ({
+    object: 'node',
+    parentId: null,
+    visible: true,
+    metadata: {},
+    children: [],
+    polygon: [],
+    holes: [],
+    holeMetadata: [],
+    height: 2.5,
+    autoFromWalls: false,
+  }),
+
+  capabilities: {
+    selectable: { hitVolume: 'bbox' },
+    surfaces: {
+      top: { height: (n) => (n as CeilingNode).height },
+    },
+    duplicable: true,
+    deletable: true,
+  },
+
+  relations: {
+    hosts: ['item'],
+    cascadeDelete: 'descendants',
+  },
+
+  parametrics: ceilingParametrics,
+
+  renderer: {
+    kind: 'parametric',
+    module: () => import('./renderer'),
+  },
+  system: {
+    module: () => import('./system'),
+    priority: 4,
+  },
+
+  toolHints: [
+    { key: 'Left click', label: 'Trace ceiling outline' },
+    { key: 'Enter', label: 'Finish ceiling' },
+    { key: 'Esc', label: 'Cancel' },
+  ],
+
+  presentation: {
+    label: 'Ceiling',
+    description: 'A polygon-bounded ceiling surface that hosts ceiling-mounted items.',
+    icon: { kind: 'iconify', name: 'lucide:square-dashed' },
+    paletteSection: 'structure',
+    paletteOrder: 40,
+  },
+
+  mcp: {
+    description: 'A polygon-bounded ceiling with optional cutout holes.',
+  },
+}