fix(backups): default S3 storage for backup schedules

Show the S3 storage selector even when S3 backups are disabled, save
storage changes immediately, and improve responsive confirmation buttons.

resources/views/components/modal-confirmation.blade.php

@@ -132,10 +132,10 @@
     @class([
         'relative h-auto',
         'w-full' => $buttonFullWidth,
-        'w-auto' => ! $buttonFullWidth,
+        'w-full sm:w-auto' => ! $buttonFullWidth,
     ])>
     @if (isset($trigger))
-        <div @click="modalOpen=true">
+        <div class="w-full" @click="modalOpen=true">
             {{ $trigger }}
         </div>
     @elseif ($customButton)