Document dependency management

### Affected version

HEAD

### Bug description

We need a better description of dependency management and transitive dependency management in Resolver 2.x. This probably needs a completely new document. I don't think any existing docs here fully address this.

Start by reviewing the existing Resolver 2.x documentation and locating any material on dependency management and transitive dependencies. Done means adding a clear, self-contained document that explains both topics without duplicating existing coverage; the issue does not name a file or test to run.

Written by the indexing model from the issue text.