plugins.database.py callers do not discriminate real errors

Callers of the plugins.database methods generally treat all errors the same as a 404.

This means that more serious errors can be missed.

Many ES commands always return a successful HTTP status, so any errors should be regarded as fatal.

For the few (e.g. GET) that can return a 4xx status, this should be explicitly checked, rather than assuming any error is 404.

In classic PonyMail, this was done by the elastic.lua interface, so callers did not have to concern themselves with this ES-specific detail.

I think it would make sense to do the checks at a lower level than currently, so the main logic does not have to concern itself with such detail.

Start by reading the callers of plugins.database.py and compare their error handling with the classic elastic.lua interface mentioned in the issue. Trace how Elasticsearch responses are classified, then verify that fatal errors are not treated as 404s while valid GET 4xx responses remain explicitly handled.

Written by the indexing model from the issue text.