[feat] Add async model upload with WebSocket progress tracking (#7746)

## Summary
- Adds asynchronous model upload support with HTTP 202 responses
- Implements WebSocket-based real-time download progress tracking via
`asset_download` events
- Creates `assetDownloadStore` for centralized download state management
and toast notifications
- Updates upload wizard UI to show "processing" state when downloads
continue in background

## Changes
- **Core**: New `assetDownloadStore` for managing async downloads with
WebSocket events
- **API**: Support for HTTP 202 async upload responses with task
tracking
- **UI**: Upload wizard now shows "processing" state and allows closing
dialog during download
- **Progress**: Periodic toast notifications (every 5s) during active
downloads with completion/error toasts
- **Schema**: Updated task statuses (`created`, `running`, `completed`,
`failed`) and WebSocket message types

## Review Focus
- WebSocket event handling and download state management in
`assetDownloadStore`
- Upload flow UX - users can now close the dialog and download continues
in background
- Toast notification frequency and timing
- Schema alignment with backend async upload API

Fixes #7748

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7746-feat-Add-async-model-upload-with-WebSocket-progress-tracking-2d36d73d3650811cb79ae06f470dcded)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/views/GraphView.vue

@@ -60,6 +60,7 @@ import { api } from '@/scripts/api'
 import { app } from '@/scripts/app'
 import { setupAutoQueueHandler } from '@/services/autoQueueService'
 import { useKeybindingService } from '@/services/keybindingService'
+import { useAssetDownloadStore } from '@/stores/assetDownloadStore'
 import { useAssetsStore } from '@/stores/assetsStore'
 import { useCommandStore } from '@/stores/commandStore'
 import { useExecutionStore } from '@/stores/executionStore'
@@ -87,6 +88,7 @@ const { t } = useI18n()
 const toast = useToast()
 const settingStore = useSettingStore()
 const executionStore = useExecutionStore()
+const assetDownloadStore = useAssetDownloadStore()
 const colorPaletteStore = useColorPaletteStore()
 const queueStore = useQueueStore()
 const assetsStore = useAssetsStore()
@@ -254,6 +256,7 @@ onMounted(() => {
   api.addEventListener('reconnecting', onReconnecting)
   api.addEventListener('reconnected', onReconnected)
   executionStore.bindExecutionEvents()
+  assetDownloadStore.setup()
 
   try {
     init()
@@ -270,6 +273,7 @@ onBeforeUnmount(() => {
   api.removeEventListener('reconnecting', onReconnecting)
   api.removeEventListener('reconnected', onReconnected)
   executionStore.unbindExecutionEvents()
+  assetDownloadStore.teardown()
 
   // Clean up page visibility listener
   if (visibilityListener) {