Server API returns string instead of array for badly-formatted tags

When tags are correctly formatted as a list in the .cook file

```
tags:
- tag1
- tag2
```
or
```
tags: [tag1, tag2]
```

the server API returns an array of strings for tags.

When for some reason though, the tags are formatted as a single string (`tags: tag1,tag2`), the API returns a single string. I think the response in that case should be an array containing a single string.

Start by locating the server API handling and serialization of recipe tags, then reproduce the response with the list and single-string .cook examples described in the issue. Done means a single-string tags value is returned as an array containing that string, while already-correct list formats remain arrays.

Written by the indexing model from the issue text.