M5-T06: add Energy device management UI and sidebar entry

frontend/src/App.tsx

@@ -10,6 +10,7 @@
  *   /                 → ProtectedRoute → AppLayout → HomePage
  *   /config           → ProtectedRoute → AppLayout → ConfigPage
  *   /records          → ProtectedRoute → AppLayout → RecordsPage
+ *   /energy           → ProtectedRoute → AppLayout → EnergyPage
  *
  * AppLayout renders a sidebar (AppSidebar) on the left; page content via <Outlet/> on the right.
  * /login and /change-password have no sidebar layout.
@@ -29,6 +30,7 @@ import { LoginPage } from './pages/LoginPage'
 import { HomePage } from './pages/HomePage'
 import { ConfigPage } from './pages/ConfigPage'
 import { RecordsPage } from './pages/RecordsPage'
+import { EnergyPage } from './pages/EnergyPage'
 import { ChangePasswordPage } from './pages/ChangePasswordPage'
 import { AppSidebar } from './components/AppSidebar'
 
@@ -125,6 +127,7 @@ export default function App() {
                 <Route index element={<HomePage />} />
                 <Route path="/config" element={<ConfigPage />} />
                 <Route path="/records" element={<RecordsPage />} />
+                <Route path="/energy" element={<EnergyPage />} />
               </Route>
             </Routes>
           </SessionProvider>