refactor(side-nav): use navigation-utils type guards

Replace inline property checks with shared type guard functions
from navigation-utils. Add keyed each iteration for stable
DOM updates when linkList changes.

Author: KATIETOLER

src/lib/components/side-nav.svelte

@@ -3,6 +3,10 @@
 
   import Navigation from '$lib/holocene/navigation/navigation-container.svelte';
   import NavigationItem from '$lib/holocene/navigation/navigation-item.svelte';
+  import {
+    isNavDividerItem,
+    isNavLinkItem,
+  } from '$lib/holocene/navigation/navigation-utils';
   import { translate } from '$lib/i18n/translate';
   import type { NavLinkListItem } from '$lib/types/global';
 
@@ -16,10 +20,10 @@
 </script>
 
 <Navigation {isCloud} {bottom} aria-label={translate('common.primary')}>
-  {#each linkList as item}
-    {#if 'divider' in item && item.divider}
+  {#each linkList as item, i (i)}
+    {#if isNavDividerItem(item)}
       <hr class="-mx-2 my-4 border-black/25" />
-    {:else if 'href' in item && !item.hidden}
+    {:else if isNavLinkItem(item) && !item.hidden}
       <NavigationItem
         link={item.href}
         label={item.label}