refactor: unify template structure by introducing a layout snippet

Replaces repetitive header, navbar, and footer code in templates with a centralized `layout` snippet for better maintainability. Cleans up and simplifies various template snippets.

site/snippets/titel.php

@@ -6,9 +6,7 @@
             </div>
             <div class="w-full max-w-lg">
                 <p class="lg:pt-0 pt-6 text-xl"><?= $page->heroText() ?></p>
-
-                <?php
-                if ($page->heroButton()->isNotEmpty()): ?>
+                <?php if ($page->heroButton()->isNotEmpty()): ?>
                     <div class="mt-6 flex flex-wrap gap-4 md:mt-8">
                         <a href="<?= $page->buttonLink() ?>" class="hover:cursor-pointer hover:text-sf_gelb-500"
                            target="_blank">
@@ -18,9 +16,7 @@
                             </button>
                         </a>
                     </div>
-                <?php
-                endif ?>
-
+                <?php endif ?>
             </div>
         </div>
     </div>