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/App.tsx

@@ -36,6 +36,7 @@ import { Settings } from "./pages/Settings";
 import { UsersPage } from "./pages/Users";
 import { FileBrowser } from "./pages/FileBrowser";
 import { Actions } from "./pages/Actions";
+import BackupsPage from "./components/BackupsPage";
 import { getAppTheme } from "./theme";
 import { getOidcConfig, isOidcConfigured, setAccessToken } from "./auth";
 import { fetchAppVersion } from "./api/client";
@@ -209,13 +210,19 @@ function Shell({
 							component={NavLink}
 							to="/actions"
 						/>
-						<Tab value="/files" label="Files" component={NavLink} to="/files" />
-						<Tab
-							value="/settings"
-							label="Settings"
-							component={NavLink}
-							to="/settings"
-						/>
+					<Tab value="/files" label="Files" component={NavLink} to="/files" />
+					<Tab
+						value="/backups"
+						label="Backups"
+						component={NavLink}
+						to="/backups"
+					/>
+					<Tab
+						value="/settings"
+						label="Settings"
+						component={NavLink}
+						to="/settings"
+					/>
 					</Tabs>
 				</Box>
 			</AppBar>
@@ -231,6 +238,7 @@ function Shell({
 					<Route path="/users" element={<UsersPage />} />
 					<Route path="/actions" element={<Actions />} />
 					<Route path="/files" element={<FileBrowser />} />
+					<Route path="/backups" element={<BackupsPage />} />
 					<Route path="/settings" element={<Settings />} />
 				</Routes>
 			</Container>