Confusing error message if using @Repository in a JDBC project

### Expected Behavior

The error should say something like:

`Cannot use a repository annotated with @Repository in a JDBC project, please use @JdbcRepository(dialect = ...) instead.`

### Actual Behaviour

The Micronaut Data docs are a bit confusing w.r.t. how to annotate repository interfaces. The docs start by saying (under "shared concepts") that you have to annotate them with `@Repository` which makes sense, but in fact if you use JDBC directly (no JPA/Hibernate) the repository must be annotated with `@JdbcRepository`. This is explained later but it's easy to miss and if you do, you get an exception with a message like this:

`No backing RepositoryOperations configured for repository. Check your configuration and try again`

This is pretty confusing. The problem isn't in the app config file, it's not clear what a "backing RepositoryOperations" is or why none is configured, and the generic "check your configuration and try again" advice is so vague it's nearly non-actionable.

### Steps To Reproduce

1. Set up a JDBC only Micronaut Data project.
2. Write a repository that inherits from e.g. `GenericRepository` and is annotated using `@Repository`
3. Run the app.
4. Be puzzled by the resulting message.

### Environment Information

_No response_

### Example Application

_No response_

### Version

4.4.4

The issue names no source file or test; start by reproducing the JDBC-only setup with a GenericRepository annotated with @Repository, then trace the resulting "No backing RepositoryOperations configured" exception. Done means the failure clearly explains that JDBC repositories should use @JdbcRepository(dialect = ...) and includes a regression test for the message.

Written by the indexing model from the issue text.