## Summary
Browsers cap live WebGL contexts per page, so each Load3D node owning
its own renderer broke once enough 3D nodes were added. All 3D views now
share a single offscreen WebGLRenderer: each view renders into the
bottom-left region of the shared drawing buffer and blits the frame into
its own plain 2D canvas, which has no context limit.
- Add sharedWebGLRenderer (refcounted singleton, grow-only buffer) and
RendererView (per-view canvas + per-view renderer state + blit)
- Per-view renderer state (tone mapping, color space, clear color) is
applied before each view renders; HDRIManager and SceneModelManager
write to it instead of the renderer
- OrbitControls/TransformControls bind to the node container explicitly
- ViewHelperManager renders the axes helper itself so it can position
and scale independently of renderer DOM layout
- RecordingManager records from the view canvas; capture renders at
exact size on the shared buffer as before
- On last view release the context is force-lost and webglcontextlost is
dispatched synchronously so context-loss handlers still run
## Screenshots (if applicable)
before
<img width="2155" height="1527" alt="image"
src="https://github.com/user-attachments/assets/35a7ab8a-28dd-41ba-8349-525bd2e97977"
/>
after
<img width="918" height="430" alt="屏幕截图 2026-07-09 135025"
src="https://github.com/user-attachments/assets/67328577-bd82-4494-921a-6d298442d081"
/>
<img width="1636" height="1509" alt="image"
src="https://github.com/user-attachments/assets/a3be9215-7cd0-427c-8264-1fd964d3ace1"
/>
