silence embeds, because they have no sound control (fixes #7854)

app/views/base/embed.scala

@@ -22,7 +22,7 @@ object embed {
           cssTagWithTheme(cssModule, config.bg)
         ),
         st.body(cls := s"base highlight ${config.board}")(
-          layout.dataSoundSet := SoundSet.default.key,
+          layout.dataSoundSet := SoundSet.silent.key,
           layout.dataAssetUrl := netConfig.assetBaseUrl,
           layout.dataAssetVersion := assetVersion.value,
           layout.dataTheme := config.bg,

modules/pref/src/main/SoundSet.scala

@@ -10,9 +10,10 @@ sealed class SoundSet private[pref] (val key: String, val name: String) {
 object SoundSet {
 
   val default = new SoundSet("standard", "Standard")
+  val silent  = new SoundSet("silent", "Silent")
 
   val list = List(
-    new SoundSet("silent", "Silent"),
+    silent,
     default,
     new SoundSet("piano", "Piano"),
     new SoundSet("nes", "NES"),