fix(theme): render sidebar active state during ssr

dcb7a755 turned hasActiveLink from a computed into a ref fed only by a
non-immediate watch and onMounted, so is-active/has-active stopped
rendering in static HTML. This broke pre-hydration sidebar highlighting
and the docsearch crawler's lvl0 selector (section.has-active div h2),
which has indexed every record as the defaultValue since then.

Run the update once during setup with the hash check skipped: the server
and the client's initial render compute identical path-only state, so
hydration stays clean; the watch and onMounted refine with the real hash
after mount.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/client/theme-default/composables/sidebar.ts

@@ -83,12 +83,14 @@ export function useSidebarItemControl(
   const isActiveLink = ref(false)
   const hasActiveLink = ref(false)
 
-  function updateActiveLink(): void {
+  function updateActiveLink(skipHashCheck = false): void {
     if (item.value.link) {
       isActiveLink.value = isActive(
         route.data.relativePath,
         route.hash,
-        item.value.link
+        item.value.link,
+        false,
+        skipHashCheck
       )
     } else {
       isActiveLink.value = false
@@ -105,15 +107,21 @@ export function useSidebarItemControl(
     hasActiveLink.value = containsActiveLink(
       route.data.relativePath,
       route.hash,
-      item.value.items
+      item.value.items,
+      skipHashCheck
     )
     if (hasActiveLink.value) {
       nextTick(() => (collapsed.value = false))
     }
   }
 
-  watch([item, route], updateActiveLink)
-  onMounted(updateActiveLink)
+  // runs during setup so active classes render in SSR output too; the hash
+  // isn't known on the server (and may differ at hydration), so it's skipped
+  // until mounted
+  updateActiveLink(true)
+
+  watch([item, route], () => updateActiveLink())
+  onMounted(() => updateActiveLink())
 
   const hasChildren = computed(() => {
     return !!(item.value.items && item.value.items.length)

src/client/theme-default/support/sidebar.ts

@@ -100,16 +100,17 @@ export function getFlatSideBarLinks(sidebar: SidebarItem[]): SidebarLink[] {
 export function hasActiveLink(
   path: string,
   hash: string,
-  items: SidebarItem | SidebarItem[]
+  items: SidebarItem | SidebarItem[],
+  skipHashCheck = false
 ): boolean {
   if (Array.isArray(items)) {
-    return items.some((item) => hasActiveLink(path, hash, item))
+    return items.some((item) => hasActiveLink(path, hash, item, skipHashCheck))
   }
-  if (items.link && isActive(path, hash, items.link)) {
+  if (items.link && isActive(path, hash, items.link, false, skipHashCheck)) {
     return true
   }
   if (items.items) {
-    return hasActiveLink(path, hash, items.items)
+    return hasActiveLink(path, hash, items.items, skipHashCheck)
   }
   return false
 }