fix: refresh image previews on media upload nodes when refreshing node definitions (#9141)

## Summary
- When pressing `R` to refresh node definitions, image previews on
LoadImage/LoadVideo nodes now update to reflect external file changes
- Re-triggers the combo widget callback to regenerate preview URLs with
a fresh cache-busting `&rand=` parameter
- Extracts `isMediaUploadComboInput` from `uploadImage.ts` to
`nodeDefSchema.ts` as a shared utility

- Fixes #2082



https://github.com/user-attachments/assets/d18d69ae-6ecd-448d-8d7c-76b2c49fdea5



## Test plan
- [ ] Open a workflow with a LoadImage node and select an image
- [ ] Edit and save the image externally (e.g. in an image editor)
- [ ] Press `R` to refresh node definitions
- [ ] Verify the preview updates to show the edited image

src/stores/imagePreviewStore.ts

@@ -388,6 +388,16 @@ export const useNodeOutputStore = defineStore('nodeOutput', () => {
     }
   }
 
+  function refreshNodeOutputs(node: LGraphNode) {
+    const locatorId = nodeToNodeLocatorId(node)
+    if (!locatorId) return
+
+    const outputs = app.nodeOutputs[locatorId]
+    if (!outputs) return
+
+    nodeOutputs.value[locatorId] = { ...outputs }
+  }
+
   function resetAllOutputsAndPreviews() {
     app.nodeOutputs = {}
     nodeOutputs.value = {}
@@ -433,6 +443,7 @@ export const useNodeOutputStore = defineStore('nodeOutput', () => {
     setNodePreviewsByExecutionId,
     setNodePreviewsByNodeId,
     updateNodeImages,
+    refreshNodeOutputs,
     syncLegacyNodeImgs,
 
     // Cleanup