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/board-view/dialogs/create-branch-dialog.tsx

@@ -13,7 +13,8 @@ import { Input } from '@/components/ui/input';
 import { Label } from '@/components/ui/label';
 import { getElectronAPI } from '@/lib/electron';
 import { toast } from 'sonner';
-import { GitBranchPlus, Loader2 } from 'lucide-react';
+import { GitBranchPlus } from 'lucide-react';
+import { Spinner } from '@/components/ui/spinner';
 
 interface WorktreeInfo {
   path: string;
@@ -133,7 +134,7 @@ export function CreateBranchDialog({
           <Button onClick={handleCreate} disabled={!branchName.trim() || isCreating}>
             {isCreating ? (
               <>
-                <Loader2 className="w-4 h-4 mr-2 animate-spin" />
+                <Spinner size="sm" className="mr-2" />
                 Creating...
               </>
             ) : (