rework email settings UX with guided flow and friendly errors

grouped providers by category, added per-provider key validation
with cross-provider detection, friendly delivery error messages,
retryable vs config error distinction, from-address in general
settings, and "Save settings" button to match admin conventions

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

lib/berrypod_web/live/admin/settings.ex

@@ -15,6 +15,7 @@ defmodule BerrypodWeb.Admin.Settings do
      |> assign(:page_title, "Settings")
      |> assign(:site_live, Settings.site_live?())
      |> assign(:cart_recovery_enabled, Settings.abandoned_cart_recovery_enabled?())
+     |> assign(:from_address, Settings.get_setting("email_from_address") || user.email)
      |> assign_stripe_state()
      |> assign_products_state()
      |> assign_account_state(user)}
@@ -108,6 +109,23 @@ defmodule BerrypodWeb.Admin.Settings do
      |> put_flash(:info, message)}
   end
 
+  # -- Events: from address --
+
+  def handle_event("save_from_address", %{"from_address" => address}, socket) do
+    address = String.trim(address)
+
+    if address != "" do
+      Settings.put_setting("email_from_address", address)
+
+      {:noreply,
+       socket
+       |> assign(:from_address, address)
+       |> put_flash(:info, "From address saved")}
+    else
+      {:noreply, put_flash(socket, :error, "From address can't be blank")}
+    end
+  end
+
   # -- Events: Stripe --
 
   def handle_event("connect_stripe", %{"stripe" => %{"api_key" => api_key}}, socket) do
@@ -415,6 +433,25 @@ defmodule BerrypodWeb.Admin.Settings do
         </div>
       </section>
 
+      <%!-- From address --%>
+      <section class="admin-section">
+        <h2 class="admin-section-title">From address</h2>
+        <p class="admin-section-desc">
+          The sender address on all emails from your shop.
+        </p>
+        <div class="admin-section-body">
+          <form phx-submit="save_from_address" class="admin-row admin-row-lg">
+            <.input
+              name="from_address"
+              value={@from_address}
+              type="email"
+              placeholder="noreply@yourshop.com"
+            />
+            <.button phx-disable-with="Saving...">Save</.button>
+          </form>
+        </div>
+      </section>
+
       <%!-- Account --%>
       <section class="admin-section">
         <h2 class="admin-section-title">Account</h2>