More forgiving connections in vue (#6565)

The previous link connection code uses
[closest](https://developer.mozilla.org/en-US/docs/Web/API/Element/closest)
to find a slot. Closest only checks parents, not siblings. Since the
sought element has no children, this meant connection to a slot required
the mouse be directly over the slot.

This is changed by finding the closest (parent) widget or slot, and then
querying for the slot. For simplicity, this means introducing an
`lg-node-widget` class. As a result, connections can be made by hovering
anywhere over a valid widget.


![vue-connections_00001](https://github.com/user-attachments/assets/e556ff3f-8cbb-4198-998d-9c2aadf2c73c)


Resolves #6488

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6565-More-forgiving-connections-in-vue-2a16d73d365081e1bf46f5d54ec382d6)
by [Unito](https://www.unito.io)

src/renderer/core/canvas/links/linkDropOrchestrator.ts

@@ -20,7 +20,9 @@ export const resolveSlotTargetCandidate = (
   const { state: dragState, setCompatibleForKey } = useSlotLinkDragUIState()
   if (!(target instanceof HTMLElement)) return null
 
-  const elWithKey = target.closest<HTMLElement>('[data-slot-key]')
+  const elWithKey = target
+    .closest('.lg-slot, .lg-node-widget')
+    ?.querySelector<HTMLElement>('[data-slot-key]')
   const key = elWithKey?.dataset['slotKey']
   if (!key) return null