feat(web): dynamic document title per route

The browser tab title was hard-coded to 'LangBot' in index.html and never
changed. Add a useDocumentTitle hook that maps the active route to an
existing i18n key and sets document.title to '<page> · LangBot', driven by
a new top-level RootLayout route element. Re-runs on navigation and on
language change so the title stays localized. Falls back to the bare app
name for unmapped routes.

web/src/app/RootLayout.tsx

@@ -0,0 +1,9 @@
+import { Outlet } from 'react-router-dom';
+import { useDocumentTitle } from '@/hooks/useDocumentTitle';
+
+// Top-level route layout: drives the dynamic document title from the active
+// route and renders the matched child route via <Outlet />.
+export default function RootLayout() {
+  useDocumentTitle();
+  return <Outlet />;
+}

web/src/hooks/useDocumentTitle.ts

@@ -0,0 +1,59 @@
+import { useEffect } from 'react';
+import { useLocation } from 'react-router-dom';
+import { useTranslation } from 'react-i18next';
+
+const APP_NAME = 'LangBot';
+
+// Map a route path to the i18n key used for its document title. Detail routes
+// reuse the section key (e.g. /home/bots and any future /home/bots/:id both
+// resolve to bots.title). Reuses existing translation keys so titles stay in
+// sync with the sidebar and page headers across all locales.
+const ROUTE_TITLE_KEYS: { match: (path: string) => boolean; key: string }[] = [
+  { match: (p) => p === '/login', key: 'common.login' },
+  { match: (p) => p === '/register', key: 'register.title' },
+  { match: (p) => p === '/reset-password', key: 'resetPassword.title' },
+  { match: (p) => p === '/wizard', key: 'sidebar.quickStart' },
+  { match: (p) => p.startsWith('/home/monitoring'), key: 'monitoring.title' },
+  { match: (p) => p.startsWith('/home/bots'), key: 'bots.title' },
+  { match: (p) => p.startsWith('/home/pipelines'), key: 'pipelines.title' },
+  {
+    match: (p) => p.startsWith('/home/add-extension'),
+    key: 'sidebar.addExtension',
+  },
+  { match: (p) => p.startsWith('/home/extensions'), key: 'plugins.title' },
+  { match: (p) => p.startsWith('/home/mcp'), key: 'mcp.title' },
+  { match: (p) => p.startsWith('/home/knowledge'), key: 'knowledge.title' },
+  { match: (p) => p.startsWith('/home/skills'), key: 'skills.title' },
+  {
+    match: (p) => p.startsWith('/home/plugin-pages'),
+    key: 'sidebar.pluginPages',
+  },
+  // /home (and anything else under it) falls back to the dashboard.
+  { match: (p) => p.startsWith('/home'), key: 'monitoring.title' },
+];
+
+/**
+ * Keeps document.title in sync with the current route, formatted as
+ * "<page> · LangBot". On routes with no specific mapping (or before i18n is
+ * ready) it falls back to the bare app name. Re-runs on navigation and on
+ * language change so the title is always localized.
+ */
+export function useDocumentTitle() {
+  const { pathname } = useLocation();
+  const { t, i18n } = useTranslation();
+
+  useEffect(() => {
+    const entry = ROUTE_TITLE_KEYS.find((e) => e.match(pathname));
+    if (!entry) {
+      document.title = APP_NAME;
+      return;
+    }
+    const pageName = t(entry.key);
+    // Guard against an unresolved key (returns the key itself) leaking into the
+    // title; fall back to the bare app name in that case.
+    document.title =
+      pageName && pageName !== entry.key
+        ? `${pageName} · ${APP_NAME}`
+        : APP_NAME;
+  }, [pathname, t, i18n.language]);
+}

web/src/router.tsx

@@ -25,11 +25,13 @@ import SkillsPage from '@/app/home/skills/page';
 import ErrorPage from '@/components/ErrorPage';
 import BackendUnavailablePage from '@/components/BackendUnavailablePage';
 import PluginPagesPage from '@/app/home/plugin-pages/page';
+import RootLayout from '@/app/RootLayout';
 
 const Loading = () => <div>Loading...</div>;
 
 export const router = createBrowserRouter([
   {
+    element: <RootLayout />,
     errorElement: <ErrorPage />,
     children: [
       {