refactor: switch render templates to partials

layouts/partials/card-btn.html

@@ -0,0 +1,8 @@
+<div class="card border-primary rounded-0 hover-shadow mb-4">
+  <a href="{{ .Permalink }}"><img class="card-img-top rounded-0" src="{{ .Params.image | relURL }}"
+      alt="{{ .Title }}"></a>
+  <div class="card-body d-flex flex-column">
+    <h4 class="card-title text-truncate mt-auto"><a href="{{ .Permalink }}">{{ .Title }}</a></h4>
+    <a href="{{ .Permalink }}" class="btn btn-primary btn-sm text-uppercase align-self-start" data-pagefind-ignore>Mehr anzeigen</a>
+  </div>
+</div>