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/list/[id]/error.tsx

@@ -0,0 +1,53 @@
+'use client'
+
+import { useEffect } from 'react'
+import { AlertTriangle } from 'lucide-react'
+import Link from 'next/link'
+
+export default function ListError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string }
+  reset: () => void
+}) {
+  useEffect(() => {
+    console.error('List page error:', error)
+  }, [error])
+
+  const isNotFound = error.message.includes('not found')
+
+  return (
+    <div className="min-h-screen flex items-center justify-center p-4 bg-gray-50">
+      <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">
+          {isNotFound ? 'List Not Found' : 'Error Loading List'}
+        </h2>
+        <p className="text-sm sm:text-base text-gray-600 text-center mb-6">
+          {isNotFound
+            ? 'The list you are looking for does not exist or has been deleted.'
+            : error.message || 'We encountered an error loading this list. Please try again.'}
+        </p>
+        <div className="flex flex-col sm:flex-row gap-3">
+          {!isNotFound && (
+            <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 tap-target"
+            >
+              Try Again
+            </button>
+          )}
+          <Link
+            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 tap-target text-center"
+          >
+            Back to Lists
+          </Link>
+        </div>
+      </div>
+    </div>
+  )
+}

app/list/[id]/item/[itemId]/error.tsx

@@ -0,0 +1,55 @@
+'use client'
+
+import { useEffect } from 'react'
+import { AlertTriangle } from 'lucide-react'
+import { useRouter } from 'next/navigation'
+
+export default function ItemError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string }
+  reset: () => void
+}) {
+  const router = useRouter()
+
+  useEffect(() => {
+    console.error('Item page error:', error)
+  }, [error])
+
+  const isNotFound = error.message.includes('not found')
+
+  return (
+    <div className="min-h-screen flex items-center justify-center p-4 bg-gray-50">
+      <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">
+          {isNotFound ? 'Item Not Found' : 'Error Loading Item'}
+        </h2>
+        <p className="text-sm sm:text-base text-gray-600 text-center mb-6">
+          {isNotFound
+            ? 'The item you are looking for does not exist or has been deleted.'
+            : error.message || 'We encountered an error loading this item. Please try again.'}
+        </p>
+        <div className="flex flex-col sm:flex-row gap-3">
+          {!isNotFound && (
+            <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 tap-target"
+            >
+              Try Again
+            </button>
+          )}
+          <button
+            onClick={() => router.back()}
+            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 tap-target"
+          >
+            Go Back
+          </button>
+        </div>
+      </div>
+    </div>
+  )
+}