WebNN support initial

src/App.tsx

@@ -444,9 +444,11 @@ export function App() {
           Model: <code>{modelId}</code> · Engine:{" "}
           {activeDevice === "webgpu"
             ? "WebGPU (on-device)"
-            : activeDevice === "wasm"
-              ? "WASM (on-device)"
-              : "on-device — backend selected on first load"}
+            : activeDevice === "webnn"
+              ? "WebNN (on-device)"
+              : activeDevice === "wasm"
+                ? "WASM (on-device)"
+                : "on-device — backend selected on first load"}
         </p>
       </footer>
     </main>