feat: update components for multi-user support

- Add sharing indicator to ListCard showing collaborator count
- Add permission badge and share button to ListDetailView
- Disable editing in ItemForm for viewers with visual feedback
- Add permission checks to item detail and edit pages
- Hide edit/delete buttons for viewers on item detail page
- Pass permission and collaborator data through component hierarchy
- Update navigation to include profile and invitations links (already done in previous tasks)

Implements task 15 from user-auth-and-sharing spec

app/list/[id]/item/[itemId]/edit/page.tsx

@@ -1,5 +1,7 @@
 import { notFound } from 'next/navigation'
 import { getItem } from '@/lib/actions'
+import { canEditList } from '@/lib/permissions'
+import { auth } from '@/auth'
 import ItemForm from '@/components/ItemForm'
 import Link from 'next/link'
 import { ArrowLeft } from 'lucide-react'
@@ -14,12 +16,20 @@ interface PageProps {
 }
 
 export default async function EditItemPage({ params }: PageProps) {
+  const session = await auth()
+  if (!session?.user?.id) {
+    notFound()
+  }
+
   const item = await getItem(params.itemId)
 
   if (!item || item.listId !== params.id) {
     notFound()
   }
 
+  // Check if user can edit this list
+  const canEdit = await canEditList(session.user.id, params.id)
+
   return (
     <main className="container mx-auto px-4 sm:px-6 py-6 sm:py-8 max-w-3xl">
       {/* Header */}
@@ -36,7 +46,7 @@ export default async function EditItemPage({ params }: PageProps) {
 
       {/* Form */}
       <div className="bg-white rounded-lg shadow-sm border border-gray-200 p-5 sm:p-6 lg:p-8">
-        <ItemForm listId={params.id} item={item} mode="edit" />
+        <ItemForm listId={params.id} item={item} mode="edit" canEdit={canEdit} />
       </div>
     </main>
   )