feat: add GM Kosteniuk section and update file structure for Verein content

Introduced a dedicated section for GM Alexandra Kosteniuk with new structured content and images. Restructured Verein-related directories, renaming and reorganizing files for improved clarity. Updated navbar to include a link to the new section. Adjusted typography and heading styles for consistency in `input.css`. Added markdown support in page blueprints.

site/blueprints/pages/blockpage.yml

@@ -7,6 +7,7 @@ fields:
     fieldsets:
       - heading
       - text
+      - markdown
       - image
       - line
       - gallery

site/snippets/navbar.php

@@ -115,6 +115,8 @@
                         </button>
                         <div class="invisible absolute left-0 z-10 mt-2 w-48 rounded-md bg-white opacity-0 shadow-lg transition-all duration-200 group-hover:visible group-hover:opacity-100">
                             <div class="py-1">
+                                <a href="/verein/gmkosteniuk"
+                                   class="block px-4 py-2 text-sm text-gray-700 hover:bg-gray-100">GM Kosteniuk</a>
                                 <a href="/verein/mitgliedschaft"
                                    class="block px-4 py-2 text-sm text-gray-700 hover:bg-gray-100">Mitgliedschaft</a>
                                 <a href="/verein/vorstand"
@@ -124,8 +126,7 @@
                                 <a href="/verein/chronik"
                                    class="block px-4 py-2 text-sm text-gray-700 hover:bg-gray-100">Chronik</a>
                                 <a href="/verein/memoriam"
-                                   class="block px-4 py-2 text-sm text-gray-700 hover:bg-gray-100">In
-                                    Memoriam</a>
+                                   class="block px-4 py-2 text-sm text-gray-700 hover:bg-gray-100">In Memoriam</a>
                             </div>
                         </div>
                     </div>
@@ -218,6 +219,8 @@
                     </svg>
                 </button>
                 <div class="mobile-dropdown-content hidden space-y-1 pl-6">
+                    <a href="/verein/gmkosteniuk"
+                       class="block px-3 py-2 text-sm text-gray-600 hover:text-blue-600">GM Kosteniuk</a>
                     <a href="/verein/mitgliedschaft"
                        class="block px-3 py-2 text-sm text-gray-600 hover:text-blue-600">Mitgliedschaft</a>
                     <a href="/verein/vorstand"