Improve real-time sync with 1-second polling and visual indicator

- Reduced polling interval from 2s to 1s for near-instant updates
- Added SyncIndicator component to show sync status
- Added console logging to debug sync behavior
- Updates across devices now appear within 1 second
- Visual feedback shows when data is being refreshed

app/list/[id]/page.tsx

@@ -7,6 +7,7 @@ import Link from 'next/link'
 import { ArrowLeft } from 'lucide-react'
 import InlineItemCreate from '@/components/InlineItemCreate'
 import ListDetailView from '@/components/ListDetailView'
+import SyncIndicator from '@/components/SyncIndicator'
 
 export const dynamic = 'force-dynamic'
 export const revalidate = 0
@@ -35,6 +36,7 @@ export default async function ListDetailPage({ params }: { params: { id: string
 
   return (
     <main className="container mx-auto px-4 sm:px-6 py-6 sm:py-8 max-w-6xl">
+      <SyncIndicator />
       {/* Header */}
       <div className="mb-6 sm:mb-8">
         <Link