add setup onboarding page, dashboard launch checklist, provider registry

- new /setup page with three-section onboarding (account, provider, payments)
- dashboard launch checklist with progress bar, go-live, dismiss
- provider registry on Provider module (single source of truth for metadata)
- payments registry for Stripe
- setup context made provider-agnostic (provider_connected, theme_customised, etc.)
- admin provider pages now fully registry-driven (no hardcoded provider names)
- auth flow: fresh installs redirect to /setup, signed_in_path respects setup state
- removed old /admin/setup wizard
- 840 tests, 0 failures

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

lib/berrypod_web/theme_hook.ex

@@ -57,8 +57,8 @@ defmodule BerrypodWeb.ThemeHook do
         {:cont, socket}
 
       not Berrypod.Accounts.has_admin?() ->
-        # Fresh install — send to registration
-        {:halt, Phoenix.LiveView.redirect(socket, to: "/users/register")}
+        # Fresh install — send to setup
+        {:halt, Phoenix.LiveView.redirect(socket, to: "/setup")}
 
       true ->
         {:halt, Phoenix.LiveView.redirect(socket, to: "/coming-soon")}