feat: bulk asset export with ZIP download (#8712)

## Summary

Adds bulk asset export with ZIP download for cloud users. When selecting
2+ assets and clicking download, the frontend now requests a server-side
ZIP export instead of triggering individual file downloads.

## Changes

### New files
- **`AssetExportProgressDialog.vue`** — HoneyToast-based progress dialog
showing per-job export status with progress percentages, error
indicators, and a manual re-download button for completed exports
- **`assetExportStore.ts`** — Pinia store that tracks export jobs,
handles `asset_export` WebSocket events for real-time progress, polls
stale exports via the task API as a fallback, and auto-triggers ZIP
download on completion

### Modified files
- **`useMediaAssetActions.ts`** — `downloadMultipleAssets` now routes to
ZIP export (via `createAssetExport`) in cloud mode when 2+ assets are
selected; single assets and OSS mode still use direct download
- **`assetService.ts`** — Added `createAssetExport()` and
`getExportDownloadUrl()` endpoints
- **`apiSchema.ts`** — Added `AssetExportWsMessage` type for the
WebSocket event
- **`api.ts`** — Wired up `asset_export` WebSocket event
- **`GraphView.vue`** — Mounted `AssetExportProgressDialog`
- **`main.json`** — Added i18n keys for export toast UI

## How it works

1. User selects multiple assets and clicks download
2. Frontend calls `POST /assets/export` with asset/job IDs
3. Backend creates a ZIP task and streams progress via `asset_export`
WebSocket events
4. `AssetExportProgressDialog` shows real-time progress
5. On completion, the ZIP is auto-downloaded via a presigned URL from
`GET /assets/exports/{name}`

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8712-feat-bulk-asset-export-with-ZIP-download-3006d73d365081839ec3dd3e7b0d3b77)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Amp <amp@ampcode.com>
Co-authored-by: GitHub Action <action@github.com>

src/scripts/api.ts

@@ -22,6 +22,7 @@ import type {
 } from '@/platform/workflow/validation/schemas/workflowSchema'
 import type {
   AssetDownloadWsMessage,
+  AssetExportWsMessage,
   CustomNodesI18n,
   EmbeddingsResponse,
   ExecutedWsMessage,
@@ -169,6 +170,7 @@ interface BackendApiCalls {
   progress_state: ProgressStateWsMessage
   feature_flags: FeatureFlagsWsMessage
   asset_download: AssetDownloadWsMessage
+  asset_export: AssetExportWsMessage
 }
 
 /** Dictionary of all api calls */