Update sidebar unit grouping and apply layout/page updates

hdyc-svelte/src/routes/+layout.svelte

@@ -265,6 +265,7 @@
   let isMobileHeader = false;
   let theme: ThemeMode = 'dark';
   let selectedPaletteIndex = 0;
+  let savedScrollRestoration: ScrollRestoration | null = null;
   $: isHomepage = $page.url.pathname === '/';
   $: if (isHomepage && (sidebarOpen || headerSearchOpen)) {
     sidebarOpen = false;
@@ -326,14 +327,30 @@
     document.head.appendChild(script);
   };
 
-  afterNavigate(() => {
+  const scrollToTop = () => {
+    if (!browser) return;
+    window.scrollTo({ top: 0, behavior: 'auto' });
+  };
+
+  afterNavigate(({ from, to, type }) => {
     sidebarOpen = false;
     headerSearchOpen = false;
+
+    if (!browser) return;
+    if (type === 'popstate') return;
+    if (!from || !to) return;
+    if (from.url.pathname === to.url.pathname) return;
+
+    scrollToTop();
   });
 
   onMount(() => {
     if (!browser) return;
     const appWindow = window as WindowWithAnalytics;
+    if ('scrollRestoration' in window.history) {
+      savedScrollRestoration = window.history.scrollRestoration;
+      window.history.scrollRestoration = 'manual';
+    }
     let idleCallbackId: number | null = null;
     let fallbackTimeoutId: number | null = null;
 
@@ -411,6 +428,9 @@
         window.clearTimeout(fallbackTimeoutId);
       }
       window.removeEventListener('keydown', handleEscape);
+      if (savedScrollRestoration !== null) {
+        window.history.scrollRestoration = savedScrollRestoration;
+      }
     };
 
     if ('addEventListener' in mediaQuery) {

hdyc-svelte/src/routes/[slug]/+page.svelte

@@ -1,8 +1,5 @@
 <script lang="ts">
   import Calculator from '$lib/components/Calculator.svelte';
-  import { afterNavigate } from '$app/navigation';
-  import { browser } from '$app/environment';
-  import { onMount } from 'svelte';
   import type { PageData } from './$types';
   import { buildSeoMeta, canonicalUrl, SITE_NAME, SITE_URL, toJsonLd } from '$lib/seo';
 
@@ -56,15 +53,6 @@
     },
   });
 
-  afterNavigate(() => {
-    if (!browser) return;
-    window.scrollTo({ top: 0 });
-  });
-
-  onMount(() => {
-    if (!browser) return;
-    window.scrollTo({ top: 0 });
-  });
 </script>
 
 <svelte:head>