fix(export): stamp openable only when an open clip bakes

A door/window only carries extras.openable + extras.clips when an open
animation actually bakes. Cased openings (no leaf) and fixed windows (no
operable sash) are no longer mislabelled openable, so the GLB never claims
a part opens when nothing moves. /viewer is unaffected (it already required
openable && clips). Adds a regression test for the no-clip case.

(Export barrels reordered by the formatter.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/viewer/src/index.ts

@@ -14,10 +14,10 @@ export { ErrorBoundary } from './components/error-boundary'
 export { NodeRenderer } from './components/renderers/node-renderer'
 export { default as Viewer, type ViewerHandle } from './components/viewer'
 export {
-  GlbScene,
   type GlbHover,
   type GlbIdentity,
   type GlbLevel,
+  GlbScene,
 } from './components/viewer/glb-scene'
 export type { HoverStyle, HoverStyles } from './components/viewer/post-processing'
 export {