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/scripts/app.ts

@@ -89,7 +89,8 @@ import {
   executeWidgetsCallback,
   createNode,
   fixLinkInputSlots,
-  isImageNode
+  isImageNode,
+  isVideoNode
 } from '@/utils/litegraphUtil'
 import {
   createSharedObjectUrl,
@@ -1822,6 +1823,7 @@ export class ComfyApp {
       this.registerNodeDef(nodeId, defs[nodeId])
     }
     // Refresh combo widgets in all nodes including those in subgraphs
+    const nodeOutputStore = useNodeOutputStore()
     forEachNode(this.rootGraph, (node) => {
       const def = defs[node.type]
       // Allow primitive nodes to handle refresh
@@ -1854,6 +1856,12 @@ export class ComfyApp {
           }
         }
       }
+
+      // Re-trigger previews on media nodes (e.g. LoadImage)
+      // to bust browser cache when files are edited externally
+      if (isImageNode(node) || isVideoNode(node)) {
+        nodeOutputStore.refreshNodeOutputs(node)
+      }
     })
 
     await useExtensionService().invokeExtensionsAsync(