This change adds the ability for crop wranglers to create and manage companion plantings for crops.
- Adds a `source_url` to the `CropCompanion` model to store an optional reference URL.
- Restricts the management of companion plantings to users with the `crop_wrangler` role.
- Creates a new admin interface for managing companion plantings for a specific crop.
- Updates the crop show page to display companions from both the crop and its parent crop.
Daniel O'Connor