[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/ModelImportProgressDialog.vue

@@ -4,6 +4,7 @@ import Popover from 'primevue/popover'
 import { computed, ref } from 'vue'
 import { useI18n } from 'vue-i18n'
 
+import Loader from '@/components/common/Loader.vue'
 import HoneyToast from '@/components/honeyToast/HoneyToast.vue'
 import ProgressToastItem from '@/components/toast/ProgressToastItem.vue'
 import Button from '@/components/ui/button/Button.vue'
@@ -175,9 +176,7 @@ function closeDialog() {
       >
         <div class="flex min-w-0 flex-1 items-center gap-2 text-sm">
           <template v-if="isInProgress">
-            <i
-              class="icon-[lucide--loader-circle] size-4 flex-shrink-0 animate-spin text-muted-foreground"
-            />
+            <Loader size="sm" class="flex-shrink-0 text-muted-foreground" />
             <span
               class="min-w-0 flex-1 truncate font-bold text-base-foreground"
             >