feat: Re-add text decoration for accessibility

src/fellchensammlung/static/fellchensammlung/css/styles.css

@@ -42,7 +42,6 @@ table {
 }
 
 a {
-    text-decoration: none;
     color: inherit;
 }
 
@@ -201,6 +200,10 @@ select, .button {
     display: block;
 }
 
+a.btn, a.btn2, a.nav-link {
+    text-decoration: none;
+}
+
 .btn2 {
     background-color: var(--secondary-light-one);
     color: var(--primary-dark-one);