feat: add toast notification setup

[dzekojohn4]

Task

Integrate react-hot-toast into the app.

Requirements

• Add <Toaster /> to src/app/layout.tsx
• Configure position: top-right
• Create a src/utils/toast.ts helper:

export const toast = {
  success: (msg: string) => hotToast.success(msg),
  error: (msg: string) => hotToast.error(msg),
  loading: (msg: string) => hotToast.loading(msg),
}

Acceptance Criteria

• Toaster renders in layout
• Success and error toasts display correctly