rework setup wizard into phased flow

phase 1 (no admin): show only the email form
phase 2 (admin created, not logged in): "check your inbox" gate with
  "wrong email? start over" link that deletes the unconfirmed user
phase 3 (logged in via magic link): show provider + stripe steps

removes the confusing redirect to /users/log-in after account creation.
users now stay on /setup throughout the entire setup process.

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

test/berrypod/accounts_test.exs

@@ -64,6 +64,47 @@ 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())
+    end
+
+    test "returns the admin email" do
+      user = user_fixture()
+      assert Accounts.admin_email() == user.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
+      user = user_fixture()
+      assert {:error, :already_confirmed} = Accounts.delete_unconfirmed_user(user)
+      assert Accounts.has_admin?()
+    end
+  end
+
   describe "register_user/1" do
     test "requires email to be set" do
       {:error, changeset} = Accounts.register_user(%{})