extract setup wizard to dedicated /admin/setup page

Move the setup stepper out of the dashboard into its own LiveView.
Dashboard now redirects to setup when site isn't live, and shows
stats-only view once live. Also cleans up button component variant
handling, fixes alert CSS, and removes stale demo.html.

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

test/berrypod_web/live/auth/confirmation_test.exs

@@ -64,7 +64,7 @@ defmodule BerrypodWeb.Auth.ConfirmationTest do
       assert Accounts.get_user!(user.id).confirmed_at
       # we are logged in now
       assert get_session(conn, :user_token)
-      assert redirected_to(conn) == ~p"/admin"
+      assert redirected_to(conn) == ~p"/admin/setup"
 
       # log out, new conn
       conn = build_conn()

test/berrypod_web/live/auth/login_test.exs

@@ -56,7 +56,7 @@ defmodule BerrypodWeb.Auth.LoginTest do
 
       conn = submit_form(form, conn)
 
-      assert redirected_to(conn) == ~p"/admin"
+      assert redirected_to(conn) == ~p"/admin/setup"
     end
 
     test "redirects to login page with a flash error if credentials are invalid", %{

test/berrypod_web/live/auth/registration_test.exs

@@ -25,7 +25,7 @@ defmodule BerrypodWeb.Auth.RegistrationTest do
         conn
         |> log_in_user(user_fixture())
         |> live(~p"/users/register")
-        |> follow_redirect(conn, ~p"/admin")
+        |> follow_redirect(conn, ~p"/admin/setup")
 
       assert {:ok, _conn} = result
     end