[refactor] Replace PrimeVue ProgressSpinner with Lucide loader icon (#9372)

## Summary
- Replace PrimeVue `ProgressSpinner` with Lucide `loader-circle` icon in
App.vue and WorkspaceAuthGate.vue
- Use white color for loading spinner for better visibility on dark
backgrounds
- Remove `primevue/progressspinner` imports and update related test

## Changes
- **App.vue**: Replace `ProgressSpinner` with
`icon-[lucide--loader-circle]`
- **WorkspaceAuthGate.vue**: Same replacement
- **WorkspaceAuthGate.test.ts**: Remove ProgressSpinner mock, use
`.animate-spin` selector

## Review Focus
- Visual consistency of white spinner on dark background during initial
load

<img width="1596" height="1189" alt="스크린샷 2026-03-04 오후 6 28 27"
src="https://github.com/user-attachments/assets/d703db74-4123-4328-912a-45ac45cf6eeb"
/>
<img width="1680" height="1304" alt="스크린샷 2026-03-04 오후 6 28 24"
src="https://github.com/user-attachments/assets/8026d10a-7e06-4f95-849c-bc891756823c"
/>

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9372-refactor-Replace-PrimeVue-ProgressSpinner-with-Lucide-loader-icon-3196d73d3650815bb1d1d4554f7f744e)
by [Unito](https://www.unito.io)

src/platform/assets/components/UploadModelFooter.vue

@@ -49,10 +49,7 @@
       :disabled="!canFetchMetadata || isFetchingMetadata"
       @click="emit('fetchMetadata')"
     >
-      <i
-        v-if="isFetchingMetadata"
-        class="icon-[lucide--loader-circle] animate-spin"
-      />
+      <Loader v-if="isFetchingMetadata" />
       <span>{{ $t('g.continue') }}</span>
     </Button>
     <Button
@@ -63,7 +60,7 @@
       :disabled="!canUploadModel || isUploading"
       @click="emit('upload')"
     >
-      <i v-if="isUploading" class="icon-[lucide--loader-circle] animate-spin" />
+      <Loader v-if="isUploading" />
       <span>{{ $t('assetBrowser.upload') }}</span>
     </Button>
     <template
@@ -109,6 +106,7 @@
 <script setup lang="ts">
 import { ref } from 'vue'
 
+import Loader from '@/components/common/Loader.vue'
 import Button from '@/components/ui/button/Button.vue'
 import VideoHelpDialog from '@/platform/assets/components/VideoHelpDialog.vue'