SelectionManager: route furnish-category registry kinds through furnish phase

Shelf clicks in 3D weren't selecting: getSelectionTarget routed shelf
(category='furnish') to the furnish phase, but furnish.isValid hard-
coded `node.type !== 'item'` and rejected shelf. Click switched phase,
nothing selected.

Fix: extend furnish.isValid to also accept registry-driven kinds whose
def.category === 'furnish' AND def.capabilities.selectable. Item's
asset.category door/window special-case stays first.

Future furnish-category kinds (tables, lamps, etc.) are selectable in
furnish phase without further changes.

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

packages/editor/src/components/editor/selection-manager.tsx

@@ -684,9 +684,19 @@ const SELECTION_STRATEGIES: Record<string, SelectionStrategy> = {
     },
     isValid: (node) => {
       if (!isNodeInCurrentLevel(node)) return false
-      if (node.type !== 'item') return false
+      // Item: door/window-category items belong to structure phase, not furnish.
+      if (node.type === 'item') {
         const item = node as ItemNode
         return item.asset.category !== 'door' && item.asset.category !== 'window'
+      }
+      // Registry-driven kinds with `category: 'furnish'` (shelf today,
+      // future furniture kinds): selectable in furnish phase if their
+      // definition declares the `selectable` capability. Without this
+      // branch, shelf clicks routed to furnish phase via getSelectionTarget
+      // would be rejected here — single-click selection broken.
+      const def = nodeRegistry.get(node.type)
+      if (def && def.category === 'furnish' && def.capabilities.selectable) return true
+      return false
     },
   },
 }