add fresh install redirect and admin provider tests

Fresh installs now redirect to /users/register instead of showing the
demo shop. Post-login redirect goes to /admin dashboard (with setup
checklist) instead of /admin/settings. Added 16 provider tests covering
index (list, delete, sync) and form (new, edit, test connection).

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

lib/simpleshop_theme_web/live/admin/providers/index.html.heex

@@ -8,7 +8,7 @@
 </.header>
 
 <div id="connections" phx-update="stream" class="mt-6 space-y-4">
-  <div class="hidden only:block text-center py-12">
+  <div id="connections-empty" class="hidden only:block text-center py-12">
     <.icon name="hero-cube" class="size-16 mx-auto mb-4 text-base-content/30" />
     <h2 class="text-xl font-medium">Connect your Printify account</h2>
     <p class="mt-2 text-base-content/60 max-w-md mx-auto">

lib/simpleshop_theme_web/theme_hook.ex

@@ -51,8 +51,8 @@ defmodule SimpleshopThemeWeb.ThemeHook do
         {:cont, socket}
 
       not SimpleshopTheme.Accounts.has_admin?() ->
-        # Fresh install — no admin yet, show the demo shop
-        {:cont, socket}
+        # Fresh install — send to registration
+        {:halt, Phoenix.LiveView.redirect(socket, to: "/users/register")}
 
       true ->
         {:halt, Phoenix.LiveView.redirect(socket, to: "/coming-soon")}

lib/simpleshop_theme_web/user_auth.ex

@@ -257,9 +257,9 @@ defmodule SimpleshopThemeWeb.UserAuth do
   end
 
   @doc "Returns the path to redirect to after log in."
-  # the user was already logged in, redirect to admin settings
+  # the user was already logged in, redirect to admin dashboard
   def signed_in_path(%Plug.Conn{assigns: %{current_scope: %Scope{user: %Accounts.User{}}}}) do
-    ~p"/admin/settings"
+    ~p"/admin"
   end
 
   def signed_in_path(_), do: ~p"/"