Disambiguate dbt's behavior when the root project and a package have the same model name

### Contributions

- [x] I have read the contribution docs, and understand what's expected of me.

### Link to the page on docs.getdbt.com requiring updates

There's a couple bits of relevant documentation about what dbt will do when there is a duplicated model name across two different packages (root dbt project and dbt package as a dependency) [[1](https://docs.getdbt.com/faqs/Project/unique-resource-names)][[2](https://docs.getdbt.com/reference/dbt-jinja-functions/ref#ref-project-specific-models)].

### What part(s) of the page would you like to see updated?

Current docs are ambiguous. Maintainers of dbt-core need to make a decision about how dbt is supposed to behave so we can clarify that in our docs. This issue will be blocked until then.

See https://github.com/dbt-labs/dbt-core/issues/11351#issuecomment-2701344466 for more detail.

### Additional information

_No response_