feat: implement core server actions for enhanced task operations

- Add updateItem server action with support for all metadata fields (title, description, completed, priority, dueDate, tags, notes)
- Add deleteItem server action with proper revalidation
- Add deleteList server action with cascade behavior (handled by Prisma schema)
- Add updateList server action for renaming and color updates

Requirements: 1.2, 1.3, 2.4, 2.5

lib/actions.ts

@@ -60,4 +60,62 @@ export async function toggleItem(itemId: string) {
   })
   revalidatePath(`/list/${item.listId}`)
   return updated
+}
+
+export async function updateItem(
+  itemId: string,
+  data: {
+    title?: string
+    description?: string | null
+    completed?: boolean
+    priority?: 'low' | 'medium' | 'high'
+    dueDate?: Date | null
+    tags?: string[]
+    notes?: string | null
+  }
+) {
+  const item = await prisma.item.findUnique({ where: { id: itemId } })
+  if (!item) return null
+
+  const updated = await prisma.item.update({
+    where: { id: itemId },
+    data,
+  })
+  revalidatePath(`/list/${item.listId}`)
+  return updated
+}
+
+export async function deleteItem(itemId: string) {
+  const item = await prisma.item.findUnique({ where: { id: itemId } })
+  if (!item) return null
+
+  await prisma.item.delete({
+    where: { id: itemId },
+  })
+  revalidatePath(`/list/${item.listId}`)
+  return { success: true }
+}
+
+export async function deleteList(listId: string) {
+  await prisma.list.delete({
+    where: { id: listId },
+  })
+  revalidatePath('/')
+  return { success: true }
+}
+
+export async function updateList(
+  listId: string,
+  data: {
+    title?: string
+    color?: string
+  }
+) {
+  const updated = await prisma.list.update({
+    where: { id: listId },
+    data,
+  })
+  revalidatePath('/')
+  revalidatePath(`/list/${listId}`)
+  return updated
 }