fix(scene): fix vertex snap not cancelling on V key release

[bofeng-song]

Related issue: https://zentao.sud.center/index.php?m=bug&f=view&bugID=414

Summary

Vertex snapping (hold V) could not be cancelled by releasing the V key — the snap gizmo stayed active after key release.

Root cause

The engine's KeyboardInputSource._handleKeyboardUp calls event.stopPropagation() on every canvas keyup event. Since input-bridge.js registered its keyup listener on document (bubble phase), the stopped propagation meant the listener never fired.

In Creator this is not an issue because the engine runs inside a separate iframe/webview, so its stopPropagation() on the inner canvas does not affect the outer document's listeners. In the CLI, the engine and input-bridge.js share the same document context.

Fix

Switch the keyup listener from a normal document listener to capture phase (addEventListener('keyup', handler, true)). Capture runs top-down (window → document → ... → canvas) before the event reaches the canvas target, so it fires before the engine can stop propagation.

Test plan

• Open scene editor, select a node with a mesh
• Hold V → vertex snap activates (floating gizmo appears at nearest vertex)
• Release V → vertex snap cancels (gizmo returns to node center, snap drag plane hides)
• Repeat while moving mouse outside the canvas area during V hold — keyup should still be captured