feat: Add visual feedback and polish (Task 15)

- Implement toast notification system for success/error messages
- Add loading states with skeleton loaders for async operations
- Create smooth CSS transitions and animations
- Enhance empty states with EmptyState component
- Add loading.tsx files for Next.js loading states
- Integrate toast notifications across all CRUD operations
- Add fade-in and scale-in animations for better UX
- Improve visual feedback for user actions

components/Toast.tsx

@@ -0,0 +1,51 @@
+'use client'
+
+import { useEffect } from 'react'
+import { CheckCircle, XCircle, AlertCircle, X } from 'lucide-react'
+
+export type ToastType = 'success' | 'error' | 'info'
+
+interface ToastProps {
+  message: string
+  type: ToastType
+  onClose: () => void
+  duration?: number
+}
+
+export default function Toast({ message, type, onClose, duration = 3000 }: ToastProps) {
+  useEffect(() => {
+    if (duration > 0) {
+      const timer = setTimeout(onClose, duration)
+      return () => clearTimeout(timer)
+    }
+  }, [duration, onClose])
+
+  const icons = {
+    success: <CheckCircle size={20} className="flex-shrink-0" />,
+    error: <XCircle size={20} className="flex-shrink-0" />,
+    info: <AlertCircle size={20} className="flex-shrink-0" />,
+  }
+
+  const styles = {
+    success: 'bg-green-50 border-green-200 text-green-800',
+    error: 'bg-red-50 border-red-200 text-red-800',
+    info: 'bg-blue-50 border-blue-200 text-blue-800',
+  }
+
+  return (
+    <div
+      className={`flex items-center gap-3 px-4 py-3 rounded-lg border shadow-lg ${styles[type]} animate-slide-in-right`}
+      role="alert"
+    >
+      {icons[type]}
+      <p className="flex-1 text-sm font-medium">{message}</p>
+      <button
+        onClick={onClose}
+        className="text-current opacity-70 hover:opacity-100 transition-opacity tap-target-sm"
+        aria-label="Close notification"
+      >
+        <X size={18} />
+      </button>
+    </div>
+  )
+}