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/components/layouts/admin.html.heex

@@ -43,14 +43,6 @@
       <%!-- nav links --%>
       <nav class="flex-1 p-2" aria-label="Admin navigation">
         <ul class="admin-nav">
-          <li :if={!@site_live}>
-            <.link
-              navigate={~p"/admin/setup"}
-              class={admin_nav_active?(@current_path, "/admin/setup")}
-            >
-              <.icon name="hero-rocket-launch" class="size-5" /> Setup
-            </.link>
-          </li>
           <li>
             <.link
               navigate={~p"/admin"}