WebNN support initial

src/components/ModelPicker.tsx

@@ -24,6 +24,7 @@ interface ModelPickerProps {
 const DEVICE_OPTIONS: readonly { value: DevicePreference; label: string }[] = [
   { value: "auto", label: "Auto (WebGPU if available)" },
   { value: "webgpu", label: "WebGPU" },
+  { value: "webnn", label: "WebNN" },
   { value: "wasm", label: "WASM (CPU)" },
 ];
 
@@ -47,7 +48,12 @@ export function ModelPicker({
   // the device. Until the worker has reported one, assume WASM unless the
   // user explicitly asked for WebGPU.
   const estimateDevice: InferenceDevice =
-    activeDevice ?? (devicePreference === "webgpu" ? "webgpu" : "wasm");
+    activeDevice ??
+    (devicePreference === "webgpu"
+      ? "webgpu"
+      : devicePreference === "webnn"
+        ? "webnn"
+        : "wasm");
 
   const groups: { title: string; items: WhisperModel[] }[] = [
     {