Moves a project from bundling .env files (readable by anyone who unzips
the app) to a generated Dart class. Previews by default; --apply makes
the changes. The client .env files themselves are never modified.
Applies a client's native branding (app name, bundle id, icons, splash)
to the project. By default the project files it touches (pubspec, icon
config, root .env, branding assets) are restored afterwards; with
--keep they stay applied so the app can be run as that client.