WebNN support initial

src/worker/inference.worker.ts

@@ -86,14 +86,22 @@ function forwardProgress(info: ProgressInfo): void {
 // Device selection (D-004): WebGPU when available, automatic WASM fallback
 // ---------------------------------------------------------------------------
 
-interface NavigatorWithGpu {
+interface NavigatorWithHardware {
   gpu?: { requestAdapter(): Promise<unknown | null> };
+  ml?: unknown;
 }
 
 async function detectDevice(preference: DevicePreference): Promise<InferenceDevice> {
   if (preference === "wasm") return "wasm";
+  if (preference === "webnn") {
+    try {
+      return (navigator as NavigatorWithHardware).ml ? "webnn" : "wasm";
+    } catch {
+      return "wasm";
+    }
+  }
   try {
-    const adapter = await (navigator as NavigatorWithGpu).gpu?.requestAdapter();
+    const adapter = await (navigator as NavigatorWithHardware).gpu?.requestAdapter();
     return adapter ? "webgpu" : "wasm";
   } catch {
     return "wasm";
@@ -127,7 +135,8 @@ async function createPipeline(
   // If WebGPU was selected but pipeline creation throws (driver quirks,
   // unsupported ops, out-of-memory), fall back to WASM automatically (D-004).
   const attempts: InferenceDevice[] =
-    detected === "webgpu" ? ["webgpu", "wasm"] : ["wasm"];
+    detected === "webgpu" ? ["webgpu", "wasm"] :
+    detected === "webnn" ? ["webnn", "wasm"] : ["wasm"];
 
   let lastError: unknown;
   for (const device of attempts) {

src/worker/protocol.ts

@@ -7,7 +7,7 @@
  */
 
 /** Devices the worker can actually run on (D-004). */
-export type InferenceDevice = "webgpu" | "wasm";
+export type InferenceDevice = "webgpu" | "wasm" | "webnn";
 
 /**
  * What the UI may request. "auto" (the default) lets the worker probe
@@ -147,7 +147,7 @@ function isOptionalString(value: unknown): value is string | undefined {
   return value === undefined || typeof value === "string";
 }
 
-const DEVICES: readonly string[] = ["webgpu", "wasm"];
+const DEVICES: readonly string[] = ["webgpu", "wasm", "webnn"];
 const DTYPES: readonly string[] = ["fp32", "fp16", "q8", "q4"];
 
 export function isInferenceDevice(value: unknown): value is InferenceDevice {