refactor: replace Loader2 with Spinner component across the application

This update standardizes the loading indicators by replacing all instances of Loader2 with the new Spinner component. The Spinner component provides a consistent look and feel for loading states throughout the UI, enhancing the user experience.

Changes include:
- Updated loading indicators in various components such as popovers, modals, and views.
- Ensured that the Spinner component is used with appropriate sizes for different contexts.

No functional changes were made; this is purely a visual and structural improvement.

apps/ui/src/components/views/settings-view/codex/codex-usage-section.tsx

@@ -1,6 +1,7 @@
 // @ts-nocheck
 import { useCallback, useEffect, useState } from 'react';
 import { Button } from '@/components/ui/button';
+import { Spinner } from '@/components/ui/spinner';
 import { RefreshCw, AlertCircle } from 'lucide-react';
 import { OpenAIIcon } from '@/components/ui/provider-icon';
 import { cn } from '@/lib/utils';
@@ -168,7 +169,7 @@ export function CodexUsageSection() {
             data-testid="refresh-codex-usage"
             title={CODEX_REFRESH_LABEL}
           >
-            <RefreshCw className={cn('w-4 h-4', isLoading && 'animate-spin')} />
+            {isLoading ? <Spinner size="sm" /> : <RefreshCw className="w-4 h-4" />}
           </Button>
         </div>
         <p className="text-sm text-muted-foreground/80 ml-12">{CODEX_USAGE_SUBTITLE}</p>