[backport cloud/1.36] [feat] Add async model upload with WebSocket progress tracking (#7887)

Backport of #7746 to `cloud/1.36`

Automatically created by backport workflow.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7887-backport-cloud-1-36-feat-Add-async-model-upload-with-WebSocket-progress-tracking-2e26d73d365081c4a060e6e88f33016d)
by [Unito](https://www.unito.io)

Co-authored-by: Luke Mino-Altherr <luke@comfy.org>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/platform/assets/components/UploadModelUrlInput.vue

@@ -55,7 +55,7 @@
         <p v-if="error" class="text-xs text-error">
           {{ error }}
         </p>
-        <p v-else class="text-foreground">
+        <p v-else-if="!flags.asyncModelUploadEnabled" class="text-foreground">
           <i18n-t keypath="assetBrowser.maxFileSize" tag="span">
             <template #size>
               <span class="font-bold italic">{{
@@ -77,6 +77,10 @@
 import InputText from 'primevue/inputtext'
 import { computed } from 'vue'
 
+import { useFeatureFlags } from '@/composables/useFeatureFlags'
+
+const { flags } = useFeatureFlags()
+
 const props = defineProps<{
   modelValue: string
   error?: string