fix: include subfolder in asset download URL for audio/video files (#8684)

## Summary

- `getAssetUrl()` was constructing `/view` URLs without the `subfolder`
query parameter, causing backend to return "file not found" for assets
stored in subfolders (common for audio/video outputs)
- Preview/playback was unaffected because it uses `preview_url` from
`ResultItemImpl.url` which correctly includes `subfolder`
- Fixed `getAssetUrl()` to include `subfolder` from
`asset.user_metadata` when present
- Simplified download functions to prefer `preview_url` (already
correct) with `getAssetUrl` as fallback

## Test plan

- [ ] Generate audio/video output (e.g. via SaveAudio node) that saves
to a subfolder
- [ ] Right-click the asset in the assets sidebar and click Download —
should download successfully
- [ ] Select multiple audio/video assets and use bulk download — should
download all
- [ ] Verify image downloads still work as before
- [ ] Verify cloud environment downloads still work (uses `preview_url`
path)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Release Notes

* **New Features**
  * Added support for organizing and downloading assets from subfolders.

* **Refactor**
* Improved asset URL generation and download handling for better
reliability and performance.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

src/platform/assets/composables/useMediaAssetActions.ts

@@ -65,15 +65,8 @@ export function useMediaAssetActions() {
 
     try {
       const filename = targetAsset.name
-      let downloadUrl: string
-
-      // In cloud, use preview_url directly (from cloud storage)
-      // In OSS/localhost, use the /view endpoint
-      if (isCloud && targetAsset.preview_url) {
-        downloadUrl = targetAsset.preview_url
-      } else {
-        downloadUrl = getAssetUrl(targetAsset)
-      }
+      // Prefer preview_url (already includes subfolder) with getAssetUrl as fallback
+      const downloadUrl = targetAsset.preview_url || getAssetUrl(targetAsset)
 
       downloadFile(downloadUrl, filename)
 
@@ -103,15 +96,8 @@ export function useMediaAssetActions() {
     try {
       assets.forEach((asset) => {
         const filename = asset.name
-        let downloadUrl: string
-
-        // In cloud, use preview_url directly (from GCS or other cloud storage)
-        // In OSS/localhost, use the /view endpoint
-        if (isCloud && asset.preview_url) {
-          downloadUrl = asset.preview_url
-        } else {
-          downloadUrl = getAssetUrl(asset)
-        }
+        // Prefer preview_url (already includes subfolder) with getAssetUrl as fallback
+        const downloadUrl = asset.preview_url || getAssetUrl(asset)
         downloadFile(downloadUrl, filename)
       })
 

src/platform/assets/utils/assetUrlUtil.ts

@@ -8,7 +8,7 @@ import { getAssetType } from './assetTypeUtil'
 
 /**
  * Get the download/view URL for an asset
- * Constructs the proper URL with filename encoding and type parameter
+ * Constructs the proper URL with filename encoding, type, and subfolder parameters
  *
  * @param asset The asset to get URL for
  * @param defaultType Default type if asset doesn't have tags (default: 'output')
@@ -23,7 +23,12 @@ export function getAssetUrl(
   defaultType: 'input' | 'output' = 'output'
 ): string {
   const assetType = getAssetType(asset, defaultType)
-  return api.apiURL(
-    `/view?filename=${encodeURIComponent(asset.name)}&type=${assetType}`
-  )
+  const subfolder = asset.user_metadata?.subfolder
+  const params = new URLSearchParams()
+  params.set('filename', asset.name)
+  params.set('type', assetType)
+  if (typeof subfolder === 'string' && subfolder) {
+    params.set('subfolder', subfolder)
+  }
+  return api.apiURL(`/view?${params}`)
 }