fix: load all pre-selected settings tabs correctly on mount

The watch(activeTab) handler loads tab data on navigation, but not on
initial mount when localStorage restores a tab. Three more gaps:

- briefing: was inside the isAdmin guard — non-admin users who last
  visited the Briefing tab would see an empty form
- users: no onMounted equivalent — admin user list never loaded
- logs: no onMounted equivalent — admin log viewer never loaded

Moves briefing outside the admin guard and adds users/logs inside it.

frontend/src/views/SettingsView.vue

@@ -522,8 +522,10 @@ onMounted(async () => {
       // base URL not configured yet
     }
     if (activeTab.value === "groups") loadGroupsPanel();
-    if (activeTab.value === "briefing") loadBriefingTab();
+    if (activeTab.value === "users") loadUsersPanel();
+    if (activeTab.value === "logs") loadLogsPanel();
   }
+  if (activeTab.value === "briefing") loadBriefingTab();
   if (activeTab.value === "apikeys") { fetchApiKeys(); loadMcpInfo(); }
 });