add admin email settings page with provider selection

Card radio component for picking email providers (SMTP, SendGrid, Mailjet, etc.)
with instant client-side switching via JS hook. Adapter configs are pre-rendered
and toggled without a server round-trip. Secrets are preserved when re-saving
with blank password fields. Includes from address field, test email sending,
and disconnect flow.

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

lib/berrypod_web/live/setup/onboarding.ex

@@ -101,7 +101,7 @@ defmodule BerrypodWeb.Setup.Onboarding do
 
   # ── Events: Provider ──
 
-  def handle_event("select_provider", %{"type" => type}, socket) do
+  def handle_event("select_provider", %{"provider_select" => %{"type" => type}}, socket) do
     {:noreply,
      socket
      |> assign(:selected_provider, type)
@@ -363,30 +363,20 @@ defmodule BerrypodWeb.Setup.Onboarding do
   attr :connecting, :boolean, required: true
 
   defp provider_section(assigns) do
+    assigns = assign(assigns, :provider_options, provider_card_options(assigns.providers))
+
     ~H"""
     <div>
       <p class="setup-hint">Choose a print-on-demand provider and connect your API key.</p>
 
-      <div class="setup-provider-grid">
-        <button
-          :for={provider <- @providers}
-          type="button"
-          phx-click={provider.status == :available && "select_provider"}
-          phx-value-type={provider.type}
-          disabled={provider.status == :coming_soon}
-          class={[
-            "setup-provider-card",
-            @selected == provider.type && "setup-provider-card-selected",
-            provider.status == :coming_soon && "setup-provider-card-disabled"
-          ]}
-        >
-          <span class="setup-provider-name">{provider.name}</span>
-          <span class="setup-provider-tagline">{provider.tagline}</span>
-          <span :if={provider.status == :coming_soon} class="setup-provider-badge">
-            Coming soon
-          </span>
-        </button>
-      </div>
+      <.form for={%{}} as={:provider_select} phx-change="select_provider">
+        <.card_radio_group
+          name="provider_select[type]"
+          value={@selected}
+          legend="Print provider"
+          options={@provider_options}
+        />
+      </.form>
 
       <%!-- API key form for selected provider --%>
       <div :if={@selected} class="setup-provider-form">
@@ -548,6 +538,22 @@ defmodule BerrypodWeb.Setup.Onboarding do
     end
   end
 
+  defp provider_card_options(providers) do
+    Enum.map(providers, fn provider ->
+      option = %{
+        value: provider.type,
+        name: provider.name,
+        description: provider.tagline
+      }
+
+      if provider.status == :coming_soon do
+        Map.merge(option, %{badge: "Coming soon", disabled: true})
+      else
+        option
+      end
+    end)
+  end
+
   defp format_error(:unauthorized), do: "That token doesn't seem to be valid"
   defp format_error(:timeout), do: "Couldn't reach the provider — try again"
   defp format_error(:provider_not_implemented), do: "This provider isn't supported yet"