Add cross-domain template copy: blog hamburger filter for shared layout.html

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/_types/blog/mobile/_filter/_hamburger.html

@@ -0,0 +1,13 @@
+<div class="md:hidden mx-2 bg-stone-200 rounded">
+
+
+  <span class="flex items-center justify-center text-stone-600 text-lg h-12 w-12 transition-transform group-open/filter:hidden self-start">
+    <i class="fa-solid fa-filter"></i>
+  </span>
+  <span>
+    <svg aria-hidden="true" viewBox="0 0 24 24"
+          class="w-12 h-12 rotate-180 transition-transform group-open/filter:block hidden self-start">
+      <path d="M6 9l6 6 6-6" fill="currentColor"/>
+    </svg>
+  </span>
+</div>