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/codex-usage-popover.tsx

@@ -2,6 +2,7 @@ import { useState, useEffect, useMemo, useCallback } from 'react';
 import { Popover, PopoverContent, PopoverTrigger } from '@/components/ui/popover';
 import { Button } from '@/components/ui/button';
 import { RefreshCw, AlertTriangle, CheckCircle, XCircle, Clock, ExternalLink } from 'lucide-react';
+import { Spinner } from '@/components/ui/spinner';
 import { cn } from '@/lib/utils';
 import { getElectronAPI } from '@/lib/electron';
 import { useAppStore } from '@/store/app-store';
@@ -333,7 +334,7 @@ export function CodexUsagePopover() {
           ) : !codexUsage ? (
             // Loading state
             <div className="flex flex-col items-center justify-center py-8 space-y-2">
-              <RefreshCw className="w-6 h-6 animate-spin text-muted-foreground/50" />
+              <Spinner size="lg" />
               <p className="text-xs text-muted-foreground">Loading usage data...</p>
             </div>
           ) : codexUsage.rateLimits ? (