feat: add tags and notes fields to Item model

prisma/schema.prisma

@@ -23,6 +23,8 @@ model Item {
   completed   Boolean   @default(false)
   priority    String    @default("medium") // low, medium, high
   dueDate     DateTime?
+  tags        Json      @default("[]")
+  notes       String?   @db.Text
   createdAt   DateTime  @default(now())
   updatedAt   DateTime  @updatedAt
   listId      String