Add artefact to project

Allow users to add artefacts to a project according to the following rules:

* Users can add any artefacts to projects they have a connection with (owner, participant, etc);
* Admin users can add artefacts to any project.

It is mandatory to create a project log every time an artefact is added to a project.

The issue names no files, tests, or entry points. Start by tracing how project–artefact associations are handled and where project logs are created; verify that connected users can add artefacts, admins can add them to any project, and every addition creates a log.

Written by the indexing model from the issue text.