Behavior: Generates a new, unpopulated content model with default field values for the specified content definition. This does not persist the content; it only creates the template structure for the client to fill in.

Authorization: Requires authentication and the user must have write or higher permission to the content definition. Read-only and Guest permissions are insufficient.

Side Effects: None. The content is not saved until a subsequent POST/PUT call.

Error Scenarios: Returns 400 Bad Request if the content definition ID refers to asset metadata or assets, if the content definition is invalid, or if the user lacks sufficient write permissions.