feat: update back button logic

Instead of saving back url in the param, save the
back url info inside session.

src/pages/index.astro

@@ -22,7 +22,7 @@ const recentPosts = sortedPosts.filter(({ data }) => !data.featured);
 
 <Layout>
   <Header />
-  <main id="main-content">
+  <main id="main-content" data-layout="index">
     <section id="hero" class="pt-8 pb-6">
       <h1 class="my-4 inline-block text-4xl font-bold sm:my-8 sm:text-5xl">
         Mingalaba
@@ -119,3 +119,13 @@ const recentPosts = sortedPosts.filter(({ data }) => !data.featured);
   </main>
   <Footer />
 </Layout>
+
+<script>
+  document.addEventListener("astro:page-load", () => {
+    const indexLayout = (document.querySelector("#main-content") as HTMLElement)
+      ?.dataset?.layout;
+    if (indexLayout) {
+      sessionStorage.setItem("backUrl", "/");
+    }
+  });
+</script>