shorten bincioactivity to ba on mobile

site/src/layouts/Base.astro

@@ -156,9 +156,10 @@ try {
     style="border-color: var(--border)"
   >
     <div class="max-w-7xl mx-auto px-4 h-12 flex items-center gap-3">
-      <!-- Logo: always visible, never shrinks -->
+      <!-- Logo: always visible, never shrinks. Full name on sm+, abbreviated on mobile. -->
       <a href={baseUrl} class="font-bold text-white tracking-tight hover:text-[--accent] transition-colors shrink-0">
-        Bincio<span class="text-[--accent]">Activity</span>
+        <span class="hidden sm:inline">Bincio<span class="text-[--accent]">Activity</span></span>
+        <span class="sm:hidden">B<span class="text-[--accent]">A</span></span>
       </a>
       {!isPublicPage && (
         <!-- Links: scroll horizontally on mobile, no visible scrollbar -->