feat(button) : anneau de focus clavier standard (.m-focus-ring) sur Button et ButtonIcon

Remplace le halo focus-visible:ring-2 ring-m-primary/50 par l'anneau outline
standard (m-primary plein, offset 2px), cohérent avec les autres composants.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/components/malio/button/Button.vue

@@ -84,7 +84,7 @@ const variantClasses = computed(() => {
 
 const mergedButtonClass = computed(() =>
   twMerge(
-    'inline-flex w-[180px] h-[38px] items-center justify-center gap-1 p-[10px] rounded-md text-base font-bold leading-[150%] transition-colors duration-150 focus:outline-none focus-visible:ring-2 focus-visible:ring-m-primary/50',
+    'inline-flex w-[180px] h-[38px] items-center justify-center gap-1 p-[10px] rounded-md text-base font-bold leading-[150%] transition-colors duration-150 m-focus-ring',
     variantClasses.value,
     props.buttonClass,
   ),