Plantuml tags in markdown document are an issue

### Issue

When I ask to add a plantuml diagram to a markdown file, aider asks if it should crete '@enduml' and the markdown document does not contain the plantuml description.

For instance, I am expecting output in the markdown file close to this:

```markdown
  ```plantuml
  @startuml Device_Lifecycle
  start
  :Device Onboarding;
  :Device Off-boarding;
  stop
  @enduml
  ```
```

