migrate remaining admin pages to inline feedback

Replace put_flash with inline feedback for form saves:
- Media library: metadata save shows "Saved" checkmark
- Product show: storefront controls save shows "Saved" checkmark
- Newsletter campaign form: draft save shows "Saved" checkmark

Page-level outcomes (uploads, deletes, async operations) remain as
flash/banner messages — these are the correct pattern for non-form
actions.

Completes Task 4 of notification overhaul.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/berrypod_web/live/admin/product_show.ex

@@ -27,6 +27,7 @@ defmodule BerrypodWeb.Admin.ProductShow do
           |> assign(:page_title, product.title)
           |> assign(:product, product)
           |> assign(:form, form)
+          |> assign(:save_status, :idle)
 
         {:ok, socket}
     end
@@ -40,7 +41,7 @@ defmodule BerrypodWeb.Admin.ProductShow do
       |> Map.put(:action, :validate)
       |> to_form(as: "product")
 
-    {:noreply, assign(socket, :form, form)}
+    {:noreply, assign(socket, form: form, save_status: :idle)}
   end
 
   @impl true
@@ -63,12 +64,12 @@ defmodule BerrypodWeb.Admin.ProductShow do
           socket
           |> assign(:product, product)
           |> assign(:form, form)
-          |> put_flash(:info, "Product updated")
+          |> assign(:save_status, :saved)
 
         {:noreply, socket}
 
       {:error, changeset} ->
-        {:noreply, assign(socket, :form, to_form(changeset, as: "product"))}
+        {:noreply, assign(socket, form: to_form(changeset, as: "product"), save_status: :error)}
     end
   end
 
@@ -206,6 +207,7 @@ defmodule BerrypodWeb.Admin.ProductShow do
             />
           </label>
           <.button type="submit" variant="primary" class="admin-btn-sm">Save</.button>
+          <.inline_feedback status={@save_status} />
         </.form>
       </div>
     </div>