Fixes and custom project inspector dogfooding

[mavimaec]

Fix WebGL viewer-reuse crash, error modal, and ghost-opacity sync; add inspector demo

Several fixes to the WebGL viewer, surfaced while building a reusable-viewer demo, plus the demo itself.

RenderScene/Scene — fix crash when loading into a reused viewer:

• RenderScene.removeScene recomputed the combined bounding box with reduce((a, b) => a.union(b)) and no guard. A scene whose geometry isn't built yet returns an undefined box (normal mid-load), so the union threw "Cannot read properties of undefined (reading 'union')" on the 2nd+ sequential load. Filter out undefined boxes before the union.
• Scene.dispose() called clear(), which re-adds the now-empty scene to the renderer, leaving a stale undefined-box scene registered after unload. That accumulation was the source of the undefined box above. dispose() now removes the scene from the renderer after clearing.

WebGL load errors — stop using the Ultra modal:

• ComponentLoader.onError reported failures with the Ultra serverFileDownloadingError ("VIM Ultra File Error"), misleading on a WebGL viewer and hiding the real cause. Add react-viewers/errors/webglFileError and use it, surfacing the underlying error message.

Ghost opacity — make it actually apply and configurable:

• The isolation.ghostOpacity StateRef hydrated from localStorage but the ghost material initialized from its own default, and the value was only pushed to the material on change — so a persisted opacity showed in the UI but never reached the material. Push the initial ghostOpacity into the adapter on mount (mirroring showGhost).
• Add an optional isolation.ghostOpacity to createViewer settings, seeded into the material once before the StateRefs initialize (a persisted slider value still takes precedence).

Demo — add a custom project inspector (src/customInspector.tsx, routed via main.tsx at ?page=inspector):

• Custom BIM tree (Room > Category > Family > Type > Element) and BIM info panel replacing the built-ins, reusing a single viewer across loads.
• Room rows visualize the room volume as a self-owned, transparent THREE mesh built from the room's actual geometry and added straight to the render scene (outside the viewer's tracking), since room geometry is opaque-authored and isRoom visibility is owned by the global showRooms flag. Multiple selected rooms are shown at once.

Also bump version to 1.0.0-beta.2.

[vim-sroberge]

Very nice, thanks Martin, great changes. And it's nice with the comments