auto-confirm admin during setup, skip email verification

Setup wizard no longer requires email delivery. Admin account is
auto-confirmed and auto-logged-in via token redirect. Adds setup
secret gate for prod (logged on boot), SMTP env var config in
runtime.exs, email_configured? helper, and admin warning banner
when email isn't set up. Includes plan files for this task and
the follow-up email settings UI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config/runtime.exs

@@ -95,33 +95,16 @@ if config_env() == :prod do
   #
   # Check `Plug.SSL` for all available options in `force_ssl`.
 
-  # ## Configuring the mailer
-  #
-  # Uncomment ONE of the blocks below and set the matching env vars.
-  # The API client is already configured in config/prod.exs (Swoosh.ApiClient.Req).
-  #
-  # Postmark (recommended):
-  #
-  #     config :berrypod, Berrypod.Mailer,
-  #       adapter: Swoosh.Adapters.Postmark,
-  #       api_key: System.get_env("POSTMARK_API_KEY")
-  #
-  # Mailgun:
-  #
-  #     config :berrypod, Berrypod.Mailer,
-  #       adapter: Swoosh.Adapters.Mailgun,
-  #       api_key: System.get_env("MAILGUN_API_KEY"),
-  #       domain: System.get_env("MAILGUN_DOMAIN")
-  #
-  # SMTP (any provider):
-  #
-  #     config :berrypod, Berrypod.Mailer,
-  #       adapter: Swoosh.Adapters.SMTP,
-  #       relay: System.get_env("SMTP_HOST"),
-  #       port: String.to_integer(System.get_env("SMTP_PORT") || "587"),
-  #       username: System.get_env("SMTP_USERNAME"),
-  #       password: System.get_env("SMTP_PASSWORD"),
-  #       tls: :if_available
+  # Mailer — configure via SMTP_HOST env var, or use the admin UI (email-settings plan)
+  if smtp_host = System.get_env("SMTP_HOST") do
+    config :berrypod, Berrypod.Mailer,
+      adapter: Swoosh.Adapters.SMTP,
+      relay: smtp_host,
+      port: String.to_integer(System.get_env("SMTP_PORT") || "587"),
+      username: System.get_env("SMTP_USERNAME"),
+      password: System.get_env("SMTP_PASSWORD"),
+      tls: :if_available
+  end
 
   # Stripe and Printify keys are stored encrypted in the database and loaded
   # at runtime by Berrypod.Secrets. No env vars needed for those.