feat(voice): add on-device Miao Zhang Gui wake word

Add an optional local wake response prompt configuration. The prompt asset is intentionally not included yet.

components/platform/src/runtime/platform_multimodal_runtime.c

@@ -177,6 +177,24 @@ bool platform_multimodal_audio_is_initialized(void)
     return multimodal_audio_is_initialized();
 }
 
+esp_err_t platform_multimodal_audio_register_pcm_observer(
+        platform_multimodal_audio_pcm_observer_t observer,
+        void *user_data)
+{
+    return multimodal_audio_register_pcm_observer(observer, user_data);
+}
+
+esp_err_t platform_multimodal_audio_unregister_pcm_observer(
+        platform_multimodal_audio_pcm_observer_t observer,
+        void *user_data,
+        int timeout_ms)
+{
+    return multimodal_audio_unregister_pcm_observer(
+            observer,
+            user_data,
+            timeout_ms);
+}
+
 esp_err_t platform_multimodal_audio_play_downstream_opus(const uint8_t *data, size_t len)
 {
     return multimodal_audio_handle_downstream_opus(data, len);