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/ToastContainer.tsx

@@ -0,0 +1,53 @@
+'use client'
+
+import { createContext, useContext, useState, useCallback, ReactNode } from 'react'
+import Toast, { ToastType } from './Toast'
+
+interface ToastMessage {
+  id: string
+  message: string
+  type: ToastType
+}
+
+interface ToastContextType {
+  showToast: (message: string, type: ToastType) => void
+}
+
+const ToastContext = createContext<ToastContextType | undefined>(undefined)
+
+export function useToast() {
+  const context = useContext(ToastContext)
+  if (!context) {
+    throw new Error('useToast must be used within ToastProvider')
+  }
+  return context
+}
+
+export function ToastProvider({ children }: { children: ReactNode }) {
+  const [toasts, setToasts] = useState<ToastMessage[]>([])
+
+  const showToast = useCallback((message: string, type: ToastType) => {
+    const id = Math.random().toString(36).substring(7)
+    setToasts((prev) => [...prev, { id, message, type }])
+  }, [])
+
+  const removeToast = useCallback((id: string) => {
+    setToasts((prev) => prev.filter((toast) => toast.id !== id))
+  }, [])
+
+  return (
+    <ToastContext.Provider value={{ showToast }}>
+      {children}
+      <div className="fixed top-4 right-4 z-50 flex flex-col gap-2 max-w-sm w-full px-4 sm:px-0">
+        {toasts.map((toast) => (
+          <Toast
+            key={toast.id}
+            message={toast.message}
+            type={toast.type}
+            onClose={() => removeToast(toast.id)}
+          />
+        ))}
+      </div>
+    </ToastContext.Provider>
+  )
+}