Stage 11: polish, cross-cutting concerns & hardening

- 11.1 MainLayout health indicator: warning MessageBar when fail2ban offline
- 11.2 formatDate utility + TimezoneProvider + GET /api/setup/timezone
- 11.3 Responsive sidebar: auto-collapse <640px, media query listener
- 11.4 PageFeedback (PageLoading/PageError/PageEmpty), BanTable updated
- 11.5 prefers-reduced-motion: disable sidebar transition
- 11.6 WorldMap ARIA: role/tabIndex/aria-label/onKeyDown for countries
- 11.7 Health transition logging (fail2ban_came_online/went_offline)
- 11.8 Global handlers: Fail2BanConnectionError/ProtocolError -> 502
- 11.9 379 tests pass, 82% coverage, ruff+mypy+tsc+eslint clean
- Timezone endpoint: setup_service.get_timezone, 5 new tests

frontend/src/App.tsx

@@ -23,6 +23,7 @@ import { FluentProvider } from "@fluentui/react-components";
 import { BrowserRouter, Navigate, Route, Routes } from "react-router-dom";
 import { lightTheme } from "./theme/customTheme";
 import { AuthProvider } from "./providers/AuthProvider";
+import { TimezoneProvider } from "./providers/TimezoneProvider";
 import { RequireAuth } from "./components/RequireAuth";
 import { MainLayout } from "./layouts/MainLayout";
 import { SetupPage } from "./pages/SetupPage";
@@ -52,7 +53,9 @@ function App(): React.JSX.Element {
             <Route
               element={
                 <RequireAuth>
-                  <MainLayout />
+                  <TimezoneProvider>
+                    <MainLayout />
+                  </TimezoneProvider>
                 </RequireAuth>
               }
             >