Studio distribution items don't have filenames

Distribution items in studios sometimes dont have a label or filename.
For example, for [this table](https://staging.nise.bbp.epfl.ch/nexus/studios/bbp/nmc/studios/https%3A%2F%2Fbbp.epfl.ch%2Fneurosciencegraph%2Fdata%2F3ba20d22-8812-474a-b397-6a13188cc599?workspaceId=https%3A%2F%2Fbbp.epfl.ch%2Fneurosciencegraph%2Fdata%2Fb69b6a12-3a60-4224-ae6c-e448176cceb8&dashboardId=https%3A%2F%2Fbbp.epfl.ch%2Fneurosciencegraph%2Fdata%2F3af76ab7-1398-4022-bd81-e155a0d90979) in studios, the resource with `@id` = `""https://bbp.epfl.ch/neurosciencegraph/data/reconstructedcell/24de2dd7-53c3-48c1-bf24-cf2eaf3abf5f""` has the following distributions. Note the lack of `name` in the first object. In the second object there is no extension. Almost all resources in this table have a similar problem:

Ideally the backend should send us the correct extension based on encoding format so in the frontend we don't rely on the filename.

```json
[
{
"@type": "DataDownload",
"contentUrl": "http://microcircuits.epfl.ch/#/article/article_3_mph",
"repository": {
"@id": "http://microcircuits.epfl.ch/#/article/article_3_mph"
}
},
{
"@type": "DataDownload",
"contentSize": {
"unitCode": "bytes",
"value": 560074
},
"contentUrl": "https://staging.nise.bbp.epfl.ch/nexus/v1/files/bbp/nmc/cbaa5bfe-897b-4c8c-b1c0-92a04d80fe34",
"digest": {
"algorithm": "SHA-256",
"value": "46b296ea4ada645e3be3c18472c1bad45bba596fc2774861246a23ea0c41d897"
},
"encodingFormat": "text/plain; charset=UTF-8",
"name": "file"
}
]
```

The issue names Studio distribution items, the backend, and the frontend, but no source file, test, or entry point. Trace how DataDownload fields such as encodingFormat and name are produced and consumed; done means distributions expose a usable label or filename with an extension derived from the encoding format so the frontend no longer depends on the filename.

Written by the indexing model from the issue text.