Add tabindex to elements for better keyboard navigation

src/components/atoms/Button.svelte

@@ -25,7 +25,7 @@
 </script>
 
 {#if tag === 'button'}
-    <button class={classes} on:click disabled={disabled}>
+    <button class={classes} tabindex="0" {disabled} on:click>
         <slot />
         <SplitText {text} clone={true} />
     </button>
@@ -35,7 +35,8 @@
         {rel} {target}
         sveltekit:prefetch={url && isExternal ? null : true}
         sveltekit:noscroll={isExternal ? null : true}
-        disabled={disabled}
+        {disabled}
+        tabindex="0"
         on:click
     >
         <slot />