feat(backups): wire up routes, nav, dashboard widget, and docs

- Add /backups route and navigation tab in App.tsx
- Add BackupDashboardWidget to Dashboard page
- Document backup monitoring feature in REQUIREMENTS.md

frontend/src/pages/Dashboard.tsx

@@ -35,6 +35,7 @@ import { NowPlaying } from "../components/NowPlaying";
 import { MonitoringOverviewTable } from "../components/MonitoringOverviewTable";
 import { SectionCard } from "../components/SectionCard";
 import { DialogFooter } from "../components/DialogFooter";
+import BackupDashboardWidget from "../components/BackupDashboardWidget";
 
 function emptyShortcut(): DashboardShortcutInput {
 	return {
@@ -444,6 +445,8 @@ export function Dashboard() {
 				<MonitoringOverviewTable overview={monitoringOverview} embedded />
 			</SectionCard>
 
+			<BackupDashboardWidget />
+
 			<ShortcutDialog
 				open={shortcutDialogOpen}
 				draft={shortcutDraft}