[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/renderer/extensions/linearMode/LinearControls.vue

@@ -5,6 +5,7 @@ import { storeToRefs } from 'pinia'
 import { computed, ref, shallowRef } from 'vue'
 import { useI18n } from 'vue-i18n'
 
+import Loader from '@/components/common/Loader.vue'
 import ScrubableNumberInput from '@/components/common/ScrubableNumberInput.vue'
 import Popover from '@/components/ui/Popover.vue'
 import Button from '@/components/ui/button/Button.vue'
@@ -266,7 +267,7 @@ defineExpose({ runButtonClick })
             </Button>
           </template>
           <template v-else>
-            <i class="icon-[lucide--loader-circle] size-4 animate-spin" />
+            <Loader size="sm" />
             <span v-text="t('queue.jobQueueing')" />
           </template>
         </div>

src/renderer/extensions/linearMode/OutputHistoryActiveQueueItem.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
 import { useI18n } from 'vue-i18n'
 
+import Loader from '@/components/common/Loader.vue'
 import Popover from '@/components/ui/Popover.vue'
 import Button from '@/components/ui/button/Button.vue'
 import { useCommandStore } from '@/stores/commandStore'
@@ -31,9 +32,7 @@ function clearQueue(close: () => void) {
           size="unset"
           class="size-10 rounded-sm bg-secondary-background flex items-center justify-center"
         >
-          <i
-            class="icon-[lucide--loader-circle] size-4 animate-spin text-muted-foreground"
-          />
+          <Loader size="sm" class="text-muted-foreground" />
         </Button>
       </template>
       <template #default="{ close }">