feat(ui): AppShell layout route — desktop rail, tablet icon rail, mobile tabs, theme toggle

frontend/src/App.tsx

@@ -1,5 +1,6 @@
 import { Navigate, Route, Routes } from "react-router-dom";
 import { AuthProvider, RequireAdmin, RequireAuth } from "./auth/AuthContext";
+import { AppShell } from "./components/app-shell";
 import { ErrorBoundary } from "./components/ErrorBoundary";
 import { Toaster } from "./components/Toaster";
 import { ThemeProvider } from "./components/theme";
@@ -17,13 +18,16 @@ export default function App() {
           <Routes>
             <Route path="/login" element={<Login />} />
             <Route
-              path="/"
               element={
                 <RequireAuth>
-                  <Shelf />
+                  <AppShell />
                 </RequireAuth>
               }
-            />
+            >
+              <Route path="/" element={<Shelf />} />
+              <Route path="/admin/users" element={<RequireAdmin><AdminUsers /></RequireAdmin>} />
+              <Route path="/admin/libraries" element={<RequireAdmin><AdminLibraries /></RequireAdmin>} />
+            </Route>
             <Route
               path="/book/:id"
               element={
@@ -32,26 +36,6 @@ export default function App() {
                 </RequireAuth>
               }
             />
-            <Route
-              path="/admin/users"
-              element={
-                <RequireAuth>
-                  <RequireAdmin>
-                    <AdminUsers />
-                  </RequireAdmin>
-                </RequireAuth>
-              }
-            />
-            <Route
-              path="/admin/libraries"
-              element={
-                <RequireAuth>
-                  <RequireAdmin>
-                    <AdminLibraries />
-                  </RequireAdmin>
-                </RequireAuth>
-              }
-            />
             <Route path="*" element={<Navigate to="/" replace />} />
           </Routes>
           <Toaster />