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/newsletter/campaign_form.ex

@@ -10,7 +10,8 @@ defmodule BerrypodWeb.Admin.Newsletter.CampaignForm do
      |> assign(:page_title, "New campaign")
      |> assign(:campaign, nil)
      |> assign(:subscriber_count, Newsletter.confirmed_subscriber_count())
-     |> assign(:form, to_form(%{"subject" => "", "body" => ""}, as: :campaign))}
+     |> assign(:form, to_form(%{"subject" => "", "body" => ""}, as: :campaign))
+     |> assign(:save_status, :idle)}
   end
 
   @impl true
@@ -42,7 +43,7 @@ defmodule BerrypodWeb.Admin.Newsletter.CampaignForm do
 
   @impl true
   def handle_event("validate", %{"campaign" => params}, socket) do
-    {:noreply, assign(socket, :form, to_form(params, as: :campaign))}
+    {:noreply, assign(socket, form: to_form(params, as: :campaign), save_status: :idle)}
   end
 
   def handle_event("save_draft", %{"campaign" => params}, socket) do
@@ -51,10 +52,10 @@ defmodule BerrypodWeb.Admin.Newsletter.CampaignForm do
         {:noreply,
          socket
          |> assign(:campaign, campaign)
-         |> put_flash(:info, "Campaign saved")}
+         |> assign(:save_status, :saved)}
 
       {:error, _changeset} ->
-        {:noreply, put_flash(socket, :error, "Please fill in subject and body")}
+        {:noreply, assign(socket, :save_status, :error)}
     end
   end
 
@@ -211,6 +212,7 @@ defmodule BerrypodWeb.Admin.Newsletter.CampaignForm do
             <.button type="submit">
               Save draft
             </.button>
+            <.inline_feedback status={@save_status} />
 
             <button
               type="button"