fix: exclude dead/offline sites from single-site search submenu

[Copilot]

With "Allow single site search" enabled, sites marked isDead: true in their definition still appeared in the single-site search submenu. The bug exists because getSortedAddedSites only surfaces ISiteUserConfig — isDead lives in ISiteMetadata (definition files) and is never cached in user config. A site added while alive retains allowSearch: true in stored config even after its definition gains isDead: true.

Changes

• Topbar.vue: Replace the synchronous getSortedAddedSites + v-if="allowSearch" pattern with a computedAsync (singleSiteSearchItems) that:
  • Pre-filters synchronously on allowSearch and isOffline (available in user config)
  • Loads site definitions in parallel via Promise.all and drops any site where siteMetadata.isDead === true

const singleSiteSearchItems = computedAsync(async () => {
  const sites = metadataStore.getSortedAddedSites.filter((site) => (site.allowSearch ?? false) && !site.isOffline);
  const results = await Promise.all(
    sites.map(async (site) => {
      const siteMetadata = await metadataStore.getSiteMetadata(site.id);
      return siteMetadata.isDead ? null : site;
    }),
  );
  return results.filter((site) => site !== null);
}, []);

This mirrors the existing logic in getSiteDefaultSearchSolution which already gates on both isOffline and isDead when building actual search execution plans.