revert: Remove accordion grouping + add AlertDialog

1. Reverted Accordion Grouping ✅
   Problem: Payment titles are editable by users
   - User renames "BNI Virtual Account" to "BNI VA 2"
   - Grouping breaks - gateway moves to new accordion
   - Confusing UX when titles change

   Solution: Back to flat list
   - All payment methods in one list
   - Titles can be edited without breaking layout
   - Simpler, more predictable behavior

2. Added AlertDialog Component ✅
   Installed: @radix-ui/react-alert-dialog
   Created: alert-dialog.tsx (shadcn pattern)

   Use for confirmations:
   - "Are you sure you want to delete?"
   - "Discard unsaved changes?"
   - "Disable payment method?"

   Example:
   <AlertDialog>
     <AlertDialogTrigger>Delete</AlertDialogTrigger>
     <AlertDialogContent>
       <AlertDialogHeader>
         <AlertDialogTitle>Are you sure?</AlertDialogTitle>
         <AlertDialogDescription>
           This action cannot be undone.
         </AlertDialogDescription>
       </AlertDialogHeader>
       <AlertDialogFooter>
         <AlertDialogCancel>Cancel</AlertDialogCancel>
         <AlertDialogAction>Delete</AlertDialogAction>
       </AlertDialogFooter>
     </AlertDialogContent>
   </AlertDialog>

Shadcn Dialog Components:
✅ Dialog - Forms, settings (@radix-ui/react-dialog)
✅ Drawer - Mobile bottom sheet (vaul)
✅ AlertDialog - Confirmations (@radix-ui/react-alert-dialog)

All three are official shadcn components!

admin-spa/package.json

@@ -11,6 +11,7 @@
     },
     "dependencies": {
         "@radix-ui/react-accordion": "^1.2.12",
+        "@radix-ui/react-alert-dialog": "^1.1.15",
         "@radix-ui/react-avatar": "^1.1.10",
         "@radix-ui/react-checkbox": "^1.3.3",
         "@radix-ui/react-dialog": "^1.1.15",