refactor: do not create duplicate tags

Todos/View/TagBarView.swift

@@ -24,7 +24,9 @@ struct TagBarView: View {
       .scaledToFit()
       TextField("Tag", text: $active)
         .onSubmit {
-          tags.append(Tag(id: active))
+          if !tags.contains(where: { $0.id.caseInsensitiveCompare(active) == .orderedSame }) {
+            tags.append(Tag(id: active))
+          }
           active = ""
         }
     }