Dev-permissive, prod-refuse-to-boot default Accrue.Auth adapter (D-40).

Environment behaviour

• :dev / :test — current_user/1 returns a stubbed %{id: "dev", email: "dev@localhost", role: :admin}. boot_check!/0 is a no-op. The require_admin_plug/0 function is a pass-through. This is deliberately wide-open so getting started is frictionless.
• :prod — boot_check!/0 raises Accrue.ConfigError with a message pointing at install docs, as long as :auth_adapter is still pointing at this module (the default). Plan 06's Accrue.Application.start/2 calls boot_check!/0 BEFORE any supervisor starts, so a production deploy with no auth fails loud.

A host that configures a real adapter (config :accrue, :auth_adapter, MyApp.Auth) bypasses the refusal entirely because boot_check!/0 checks the currently-configured adapter before raising.

Test seam: do_boot_check!/1

boot_check!/0 is the public API — it reads the env via Application.get_env(:accrue, :env, Mix.env()) and delegates to a private/testable do_boot_check!/1 helper. The helper is exposed (def, not defp, with @doc false) so tests can simulate the :prod branch without tampering with Application.put_env(:accrue, :env, :prod) (which bleeds between async tests and has been a source of Heisenbugs historically).