## Summary
Fix deterministic DOM widget clip-path rendering to resolve the flaky
"Can drag node" screenshot test.
## Root Cause
`useDomClipping.updateClipPath()` schedules clip-path calculation in a
`requestAnimationFrame`, but `DomWidget.vue`'s watcher reads
`clippingStyle.value` synchronously before the RAF fires. The stale
clip-path gets baked into `style.value` and never updated when the RAF
completes, causing the textarea DOM widget to non-deterministically
render in front of or behind the canvas-drawn node selection border.
## Fix
- Extract `composeStyle()` function and add a dedicated watcher on
`clippingStyle` that recomposes the final inline style whenever the
RAF-deferred clip-path updates
- Add `enableDomClipping` to the main watcher dependency array so
toggling the clipping setting immediately recomposes the style
- Add `moveMouseToEmptyArea()` call in the test as a secondary
stabilizer against hover highlight non-determinism
- Delete stale snapshot so CI regenerates it with correct clip-path
behavior
- Fixes#4658
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