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>

test/berrypod/accounts_test.exs

@@ -64,44 +64,34 @@ defmodule Berrypod.AccountsTest do
     end
   end
 
-  describe "admin_email/0" do
-    test "returns nil when no users exist" do
-      assert is_nil(Accounts.admin_email())
+  describe "register_and_confirm_admin/1" do
+    test "creates a confirmed admin user" do
+      email = unique_user_email()
+      assert {:ok, user} = Accounts.register_and_confirm_admin(%{email: email})
+      assert user.email == email
+      assert user.confirmed_at
     end
 
-    test "returns the admin email" do
-      user = user_fixture()
-      assert Accounts.admin_email() == user.email
+    test "fails if admin already exists" do
+      user_fixture()
+
+      assert {:error, :admin_already_exists} =
+               Accounts.register_and_confirm_admin(%{email: unique_user_email()})
+    end
+
+    test "validates email" do
+      assert {:error, changeset} = Accounts.register_and_confirm_admin(%{email: "bad"})
+      assert errors_on(changeset).email
     end
   end
 
-  describe "get_unconfirmed_admin/0" do
-    test "returns nil when no users exist" do
-      assert is_nil(Accounts.get_unconfirmed_admin())
-    end
-
-    test "returns unconfirmed user" do
-      user = unconfirmed_user_fixture()
-      assert Accounts.get_unconfirmed_admin().id == user.id
-    end
-
-    test "returns nil for confirmed user" do
-      _user = user_fixture()
-      assert is_nil(Accounts.get_unconfirmed_admin())
-    end
-  end
-
-  describe "delete_unconfirmed_user/1" do
-    test "deletes an unconfirmed user" do
-      user = unconfirmed_user_fixture()
-      assert {:ok, _} = Accounts.delete_unconfirmed_user(user)
-      refute Accounts.has_admin?()
-    end
-
-    test "refuses to delete a confirmed user" do
+  describe "generate_login_token/1" do
+    test "creates a login token for the user" do
       user = user_fixture()
-      assert {:error, :already_confirmed} = Accounts.delete_unconfirmed_user(user)
-      assert Accounts.has_admin?()
+      token = Accounts.generate_login_token(user)
+      assert is_binary(token)
+      assert found_user = Accounts.get_user_by_magic_link_token(token)
+      assert found_user.id == user.id
     end
   end