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/LoadingSpinner.tsx

@@ -0,0 +1,33 @@
+'use client'
+
+interface LoadingSpinnerProps {
+  size?: 'sm' | 'md' | 'lg'
+  className?: string
+}
+
+export default function LoadingSpinner({ size = 'md', className = '' }: LoadingSpinnerProps) {
+  const sizeClasses = {
+    sm: 'w-4 h-4 border-2',
+    md: 'w-6 h-6 border-2',
+    lg: 'w-8 h-8 border-3',
+  }
+
+  return (
+    <div
+      className={`${sizeClasses[size]} border-gray-300 border-t-blue-500 rounded-full animate-spin ${className}`}
+      role="status"
+      aria-label="Loading"
+    />
+  )
+}
+
+export function LoadingOverlay({ message = 'Loading...' }: { message?: string }) {
+  return (
+    <div className="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50 backdrop-blur-sm">
+      <div className="bg-white rounded-lg p-6 sm:p-8 shadow-xl flex flex-col items-center gap-4">
+        <LoadingSpinner size="lg" />
+        <p className="text-gray-700 font-medium text-sm sm:text-base">{message}</p>
+      </div>
+    </div>
+  )
+}