Slot functionality for vue nodes (#5628)

Allows for simple slot functionality in vue nodes mode.

Has:
- Drag new link from slot
- Connect new link from dropping on slot

Now:
- Tests

After:
- Drop on reroute
- Correct link color on connect
- Drop on node
- Hover effects

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5628-Slot-functionality-for-vue-nodes-2716d73d365081c59a3cef7c8a5e539e)
by [Unito](https://www.unito.io)

---------

Co-authored-by: bymyself <cbyrne@comfy.org>
Co-authored-by: AustinMroz <austin@comfy.org>
Co-authored-by: Claude <noreply@anthropic.com>

src/renderer/extensions/vueNodes/composables/useSlotElementTracking.ts

@@ -150,7 +150,6 @@ export function useSlotElementTracking(options: {
       (el) => {
         if (!el) return
 
-        // Ensure node entry
         const node = nodeSlotRegistryStore.ensureNode(nodeId)
 
         if (!node.stopWatch) {
@@ -184,6 +183,8 @@ export function useSlotElementTracking(options: {
 
         // Register slot
         const slotKey = getSlotKey(nodeId, index, type === 'input')
+
+        el.dataset.slotKey = slotKey
         node.slots.set(slotKey, { el, index, type })
 
         // Seed initial sync from DOM
@@ -203,12 +204,15 @@ export function useSlotElementTracking(options: {
 
     // Remove this slot from registry and layout
     const slotKey = getSlotKey(nodeId, index, type === 'input')
-    node.slots.delete(slotKey)
+    const entry = node.slots.get(slotKey)
+    if (entry) {
+      delete entry.el.dataset.slotKey
+      node.slots.delete(slotKey)
+    }
     layoutStore.deleteSlotLayout(slotKey)
 
     // If node has no more slots, clean up
     if (node.slots.size === 0) {
-      // Stop the node-level watcher when the last slot is gone
       if (node.stopWatch) node.stopWatch()
       nodeSlotRegistryStore.deleteNode(nodeId)
     }