fix(a11y): add tabindex to main content

Add tabindex="-1" to the #main-content container so it can receive focus when using the skip-link feature.

Author: MatteoGabriele

app/app.vue

@@ -127,7 +127,7 @@ if (import.meta.client) {
 
     <AppHeader :show-logo="!isHomepage" />
 
-    <div id="main-content" class="flex-1 flex flex-col">
+    <div id="main-content" class="flex-1 flex flex-col" tabindex="-1">
       <NuxtPage />
     </div>