Implement comprehensive error handling

- Add try-catch blocks to all server actions with retry logic
- Implement exponential backoff retry mechanism for database operations
- Add input validation to all server actions
- Create ErrorBoundary component for React error handling
- Add page-level error handlers (error.tsx, global-error.tsx)
- Add route-specific error pages for list and item routes
- Enhance database connection with graceful error handling
- Add user-friendly error messages throughout the application
- Implement proper error logging for debugging

Task: 16. Implement error handling
Requirements: All (error handling is cross-cutting)

app/global-error.tsx

@@ -0,0 +1,50 @@
+'use client'
+
+import { useEffect } from 'react'
+import { AlertTriangle } from 'lucide-react'
+
+export default function GlobalError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string }
+  reset: () => void
+}) {
+  useEffect(() => {
+    console.error('Global error:', error)
+  }, [error])
+
+  return (
+    <html lang="en">
+      <body className="bg-gray-50 min-h-screen">
+        <div className="min-h-screen flex items-center justify-center p-4">
+          <div className="max-w-md w-full bg-white rounded-lg shadow-lg p-6 sm:p-8">
+            <div className="flex items-center justify-center w-12 h-12 sm:w-16 sm:h-16 bg-red-100 rounded-full mx-auto mb-4">
+              <AlertTriangle className="w-6 h-6 sm:w-8 sm:h-8 text-red-600" />
+            </div>
+            <h2 className="text-xl sm:text-2xl font-bold text-gray-900 text-center mb-2">
+              Application Error
+            </h2>
+            <p className="text-sm sm:text-base text-gray-600 text-center mb-6">
+              A critical error occurred. Please refresh the page or contact support if the problem persists.
+            </p>
+            <div className="flex flex-col sm:flex-row gap-3">
+              <button
+                onClick={reset}
+                className="flex-1 px-4 py-3 bg-blue-500 hover:bg-blue-600 active:bg-blue-700 text-white rounded-lg transition-colors font-medium text-sm sm:text-base"
+              >
+                Try Again
+              </button>
+              <button
+                onClick={() => window.location.href = '/'}
+                className="flex-1 px-4 py-3 bg-gray-200 hover:bg-gray-300 active:bg-gray-400 text-gray-700 rounded-lg transition-colors font-medium text-sm sm:text-base"
+              >
+                Go Home
+              </button>
+            </div>
+          </div>
+        </div>
+      </body>
+    </html>
+  )
+}