MUST be used when migrating an existing React app to Flows, or when no Flows auth is wired up. Detects classic vs Apps API flow from `app.json` `infra` field, installs the right packages, and wires up the entry file. No-op when a valid auth setup is already in place. Triggers: migrate to Flows, add Flows auth, DuneAuthProvider, AppSdkAuthProvider, connectToHostApp, useDune, Flows setup, setup auth, missing auth provider, CDF authentication, Fusion iframe auth.