broken API endpoints

### Context

I am exploring the Refine.Bio API to try and get raw data for individual samples.

### Problem or idea

I have encountered a number of problems with the API:

1. The [samples endpoint](https://api.refine.bio/v1/samples/) produces a 500 error instead of a paginated list of samples.

2. The [computed files endpoint](https://api.refine.bio/v1/computed_files/) produces a 404 instead of a paginated list of computed files. Attempting to access a specific file (e.g. https://api.refine.bio/v1/computed_files/?id=5357478) produces a 500.

~~3. source_url is missing from the [search endpoint](https://api.refine.bio/v1/search/?organism=homo_sapiens) although the documentation claims that this is a required return field.~~

edit: point 3 was user error on my part

### Solution or next step

Resolve the problem so that either data or proper error codes are returned from the above endpoints.

Start by reproducing the requests against /v1/samples/ and /v1/computed_files/, including the request for a specific computed file, and inspect the handlers for these endpoints. Determine why they return 500 or 404 instead of paginated data or an appropriate error response. Done means the reported requests return the expected data or proper error codes.

Written by the indexing model from the issue text.