fix: Hide delete button for input assets in OSS and fix cloud download (#6697)

## Summary
Fix delete button visibility for input assets in OSS environment and
resolve 404 error when downloading assets in cloud.

## Changes

### 1. Improved Delete Button Visibility Logic
- **Problem**: In OSS environment, input files are sourced from local
folders and cannot be deleted
- **Solution**: Added `shouldShowDeleteButton` computed property to
conditionally hide delete buttons
- **Impact**: 
  - Input tab + Cloud: Delete button shown ✅
  - Input tab + OSS: Delete button hidden ❌
  - Output tab (all environments): Delete button shown ✅

### 2. Fixed Cloud Download 404 Error
- **Problem**: Downloading files from imported tab in cloud returned 404
error for `/api/view` endpoint
- **Root Cause**: In cloud environment, files are stored in external
storage (e.g., GCS) and `/api/view` endpoint is not available
- **Solution**: 
  - Cloud: Use `preview_url` directly for downloads
  - OSS/localhost: Continue using `/api/view` endpoint as before
- Applied the same logic to both single and bulk download operations

## Test Plan
- [ ] Verify delete button is hidden in input tab on OSS environment
- [ ] Verify delete button is shown in input tab on cloud environment
- [ ] Verify file downloads work correctly in cloud for both input and
output tabs
- [ ] Verify file downloads work correctly in OSS for output tab

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <noreply@anthropic.com>

src/platform/assets/composables/useMediaAssetActions.ts

@@ -25,11 +25,19 @@ export function useMediaAssetActions() {
     if (!asset) return
 
     try {
-      const assetType = asset.tags?.[0] || 'output'
       const filename = asset.name
-      const downloadUrl = api.apiURL(
-        `/view?filename=${encodeURIComponent(filename)}&type=${assetType}`
-      )
+      let downloadUrl: string
+
+      // In cloud, use preview_url directly (from cloud storage)
+      // In OSS/localhost, use the /view endpoint
+      if (isCloud && asset.src) {
+        downloadUrl = asset.src
+      } else {
+        const assetType = asset.tags?.[0] || 'output'
+        downloadUrl = api.apiURL(
+          `/view?filename=${encodeURIComponent(filename)}&type=${assetType}`
+        )
+      }
 
       downloadFile(downloadUrl, filename)
 
@@ -58,11 +66,19 @@ export function useMediaAssetActions() {
 
     try {
       assets.forEach((asset) => {
-        const assetType = asset.tags?.[0] || 'output'
         const filename = asset.name
-        const downloadUrl = api.apiURL(
-          `/view?filename=${encodeURIComponent(filename)}&type=${assetType}`
-        )
+        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 {
+          const assetType = asset.tags?.[0] || 'output'
+          downloadUrl = api.apiURL(
+            `/view?filename=${encodeURIComponent(filename)}&type=${assetType}`
+          )
+        }
         downloadFile(downloadUrl, filename)
       })