Hide Theme Toggle Button on Small Screens

- ADDED d-none d-md-flex classes to the theme toggle button's list item, ensuring it is hidden on small screens and only visible on medium and larger devices.
- REMOVED d-flex align-items-center classes from the same element, which previously made the button visible on all screen sizes.

Signed-off-by: Leonid Petrov <lenia.petrov@gmail.com>

Author: lenis2000

_includes/navbar.html

@@ -71,7 +71,7 @@
     {% endfor %}
     </ul>
     <ul class="navbar-nav ms-auto align-items-center">
-      <li class="nav-item d-flex align-items-center">
+      <li class="nav-item d-none d-md-flex align-items-center">
         <button class="theme-toggle-dual me-2" id="theme-toggle" title="Toggle dark mode">
           <span class="toggle-track">
             <i class="fas fa-cloud-sun"></i>