Fix cursor component triggering clicks on wrong controller's hovered entity in VR

[vincentfretin]

Description:

You can reproduce the issue on https://aframe.io/aframe/examples/showcase/ui/ that is using the laser-controls component.

When using two controllers in VR with laser-controls, the cursor component listens to WebXR session events (selectstart, selectend) which fire globally for any input source. Without filtering by handedness:

1. Left controller hovers over an image
2. Right controller hovers over the floor
3. User presses trigger on right controller
4. Click event fires on the image (wrong!) because left cursor's intersectedEl was used

Changes proposed:

• Added hand schema property to cursor component
• Filter selectstart events in onCursorDown by comparing evt.inputSource.handedness with configured hand
• Filter selectend events in onCursorUp similarly
• laser-controls now passes its hand property to the cursor component

PR done with the help of Claude Code with Opus 4.5

[dmarcos]

Thank you