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>

lib/berrypod_web/live/admin/product_show.ex

@@ -203,7 +203,7 @@ defmodule BerrypodWeb.Admin.ProductShow do
               placeholder="e.g. Apparel"
             />
           </label>
-          <.button type="submit" class="admin-btn-sm admin-btn-primary">Save</.button>
+          <.button type="submit" variant="primary" class="admin-btn-sm">Save</.button>
         </.form>
       </div>
     </div>