Buzz cannot discover projects in subfolders of the configured code directory

## Problem

Buzz cannot find projects that are stored in subfolders beneath the configured code directory.

For example, if Buzz is configured to look in:

```
~/code/
```

and the repositories are organized like this:

```
~/code/client/web-app/.git
~/code/client/mobile-app/.git
~/code/projects/buzz-tools/.git
```

Buzz does not discover those repositories because they are nested below the configured root.

## Reproduction

1. Configure Buzz to search a code directory such as `~/code`.
2. Organize repositories inside one or more subfolders, such as `~/code/client/my-app` or `~/code/projects/my-tool`.
3. Ask Buzz to find or open the projects.
4. Observe that repositories in the nested folders are missing.

## Expected behavior

Buzz should recursively discover Git repositories beneath the configured code directory, including repositories inside reasonable nested folder structures.

The search should avoid scanning unrelated or excessively deep paths as appropriate, but users should not need to flatten their code organization.

## Impact

The current workaround is to create symlinks for every nested repository directly under `~/code`. This is hacky, pollutes the folder, and becomes difficult to maintain as the number of projects grows.