improve backup button responsiveness and disable handling

Use async message passing for create_backup to update UI immediately.
Add phx-throttle and pointer-events:none to fully prevent double-clicks.

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

assets/css/admin/components.css

@@ -187,7 +187,7 @@
   color: var(--t-text-inverse);
 
   &:hover { opacity: 0.85; }
-  &:disabled { opacity: 0.5; cursor: not-allowed; }
+  &:disabled { opacity: 0.5; cursor: not-allowed; pointer-events: none; }
 }
 
 .admin-btn-primary {

lib/berrypod_web/live/admin/backup.ex

@@ -40,25 +40,11 @@ defmodule BerrypodWeb.Admin.Backup do
   end
 
   def handle_event("create_backup", _params, socket) do
-    # Ignore if already creating
     if socket.assigns.create_backup_status == :saving do
       {:noreply, socket}
     else
-      socket = assign(socket, :create_backup_status, :saving)
-
-      case Backup.create_backup() do
-        {:ok, _path} ->
-          {:noreply,
-           socket
-           |> assign(:backups, Backup.list_backups())
-           |> assign(:create_backup_status, :saved)}
-
-        {:error, error} ->
-          {:noreply,
-           socket
-           |> assign(:create_backup_status, :error)
-           |> put_flash(:error, "Failed to create backup: #{inspect(error)}")}
-      end
+      send(self(), :do_create_backup)
+      {:noreply, assign(socket, :create_backup_status, :saving)}
     end
   end
 
@@ -186,6 +172,22 @@ defmodule BerrypodWeb.Admin.Backup do
   end
 
   @impl true
+  def handle_info(:do_create_backup, socket) do
+    case Backup.create_backup() do
+      {:ok, _path} ->
+        {:noreply,
+         socket
+         |> assign(:backups, Backup.list_backups())
+         |> assign(:create_backup_status, :saved)}
+
+      {:error, error} ->
+        {:noreply,
+         socket
+         |> assign(:create_backup_status, :error)
+         |> put_flash(:error, "Failed to create backup: #{inspect(error)}")}
+    end
+  end
+
   def handle_info(:do_restore, socket) do
     backup_path = socket.assigns.uploaded_backup.path
 
@@ -329,6 +331,7 @@ defmodule BerrypodWeb.Admin.Backup do
             <button
               type="button"
               phx-click="create_backup"
+              phx-throttle="1000"
               class="admin-btn admin-btn-primary admin-btn-sm"
               disabled={@create_backup_status == :saving}
             >